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| * libbb/yescrypt: remove redundant SHA256 HMAC implementationDenys Vlasenko2025-07-071-1/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | function old new delta hmac_blocks - 88 +88 static.PBKDF2_SHA256 176 213 +37 yescrypt_kdf32_body 1046 1052 +6 static.smix 759 762 +3 hmac_block 88 64 -24 HMAC_SHA256_Final 53 - -53 HMAC_SHA256_Buf 58 - -58 HMAC_SHA256_Init 159 - -159 ------------------------------------------------------------------------------ (add/remove: 1/3 grow/shrink: 3/1 up/down: 134/-294) Total: -160 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: factor out HMAC code from TLSDenys Vlasenko2025-07-071-8/+32
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | function old new delta hmac_block - 88 +88 hmac_peek_hash - 61 +61 hmac_end - 50 +50 hmac_begin 140 177 +37 hmac_hash_v - 30 +30 .rodata 105799 105787 -12 hmac_sha_precomputed 54 - -54 hmac_sha_precomputed_v 69 - -69 hmac 83 - -83 ------------------------------------------------------------------------------ (add/remove: 5/3 grow/shrink: 1/1 up/down: 266/-218) Total: 48 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb/yescrypt: use common ascii64 encoding routineDenys Vlasenko2025-07-061-0/+1
| | | | | | | | | | | | | | | | | | | | function old new delta num2str64_lsb_first 33 46 +13 yescrypt_r 1235 1133 -102 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/1 up/down: 13/-102) Total: -89 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb/yescrypt: use common ACSII char-to-64 conversion codeDenys Vlasenko2025-07-061-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | function old new delta a2i64 - 46 +46 yescrypt_r 1215 1235 +20 decode64_uint32 167 177 +10 atoi64 25 - -25 ascii_to_bin 53 - -53 static.atoi64_partial 77 - -77 ------------------------------------------------------------------------------ (add/remove: 1/3 grow/shrink: 2/0 up/down: 76/-155) Total: -79 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb/yescrypt: code shrinkDenys Vlasenko2025-07-061-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | static.PBKDF2_SHA256 - 189 +189 HMAC_SHA256_Init - 159 +159 HMAC_SHA256_Buf - 58 +58 HMAC_SHA256_Final - 53 +53 i2a64 - 42 +42 yescrypt_r 1221 1215 -6 yescrypt_kdf32_body 1064 1046 -18 i64c 42 - -42 libcperciva_HMAC_SHA256_Final 53 - -53 libcperciva_HMAC_SHA256_Buf 58 - -58 ascii64 65 - -65 libcperciva_HMAC_SHA256_Init 159 - -159 PBKDF2_SHA256 386 - -386 ------------------------------------------------------------------------------ (add/remove: 5/6 grow/shrink: 0/2 up/down: 501/-787) Total: -286 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * Move "sha256-hash a memory array and produce the digest" helper to libbbDenys Vlasenko2025-07-061-0/+1
| | | | | | | | Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: add yescrypt password hashing supportDenys Vlasenko2025-07-061-8/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It seems to work, but not at all optimized for size. The extra copy of sha256 code need to be removed. The yescrypt code in libbb/yescrypt/* is adapted from libxcrypt-4.4.38 with minimal edits, hopefully making it easier to track backports by resetting the tree to this commit, then comparing changes in upstream libxcrypt to the tree. function old new delta blockmix_xor_save - 7050 +7050 static.blockmix_xor - 6475 +6475 blockmix - 3390 +3390 SHA256_Transform - 3083 +3083 yescrypt_kdf_body - 1724 +1724 PBKDF2_SHA256 - 1003 +1003 smix1 - 960 +960 yescrypt_r - 890 +890 salsa20 - 804 +804 smix - 790 +790 smix2 - 659 +659 blockmix_salsa8_xor - 601 +601 yescrypt_kdf - 479 +479 blockmix_salsa8 - 415 +415 Krnd - 256 +256 _HMAC_SHA256_Init - 213 +213 _SHA256_Update - 198 +198 _SHA256_Final - 195 +195 decode64_uint32 - 166 +166 encode64 - 153 +153 decode64 - 136 +136 libcperciva_HMAC_SHA256_Buf - 132 +132 SHA256_Pad_Almost - 131 +131 salsa20_simd_unshuffle - 101 +101 salsa20_simd_shuffle - 101 +101 yes_crypt - 90 +90 libcperciva_SHA256_Buf - 86 +86 crypt_make_rand64encoded - 85 +85 static.atoi64_partial - 77 +77 alloc_region - 72 +72 ascii64 - 65 +65 PAD - 64 +64 _HMAC_SHA256_Final - 55 +55 static.cpu_to_be32_vect - 51 +51 free_region - 47 +47 libcperciva_SHA256_Init - 37 +37 yescrypt_init_local - 34 +34 crypt_make_pw_salt 92 125 +33 initial_state - 32 +32 .rodata 105771 105803 +32 atoi64 - 25 +25 explicit_bzero - 22 +22 pw_encrypt 920 941 +21 yescrypt_free_local - 9 +9 crypt_make_salt 85 - -85 ------------------------------------------------------------------------------ (add/remove: 43/1 grow/shrink: 3/0 up/down: 31042/-85) Total: 30957 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | Merge branch 'busybox' into mergeRon Yorston2025-08-101-25/+8
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| * shell: update HISTFILESIZE code to be actually usefulDenys Vlasenko2025-07-031-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | "HISTFILESIZE=0" in profile wasn't working as intended, "unset HISTFILE" wasn't preventing creation of history files Now: HISTSIZE=n allows to reduce in-memory history buffer HISTFILESIZE=n allows to reduce history file size (0: truncate it) unset HISTFILE allows to not save history file at all function old new delta exitshell 138 194 +56 hush_exit 97 143 +46 save_history 266 296 +30 hush_main 1170 1186 +16 .rodata 105762 105771 +9 load_history 246 254 +8 size_from_HISTFILESIZE 44 41 -3 read_line_input 2746 2712 -34 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 6/2 up/down: 165/-37) Total: 128 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * shell: fix race between signal handlers setting bb_got_signal and poll()Denys Vlasenko2025-07-021-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | function old new delta __ppoll_time64 - 211 +211 check_got_signal_and_poll - 164 +164 read_key 607 601 -6 shell_builtin_read 1328 1318 -10 ------------------------------------------------------------------------------ (add/remove: 4/0 grow/shrink: 0/2 up/down: 375/-16) Total: 359 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: Prevent clang from reading the G pointer before it is assignedBin Meng2025-07-011-19/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It was observed that getty crashes on RISC-V 64-bit target, with the busybox binary compiled by clang/LLVM 17 with -O2. Not only getty, but also some other applets like syslogd/vi are broken too. Commit 5156b245 ("Make const ptr assign as function call in clang") introduced XZALLOC_CONST_PTR() to defeat the compiler optimization, however it only fixed a small number of broken places when compiling busybox with clang/LLVM. A large number of places remain broken. This commit treats ASSIGN_CONST_PTR() the same way as XZALLOC_CONST_PTR(). Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | tls: whitespace fixesRon Yorston2025-08-081-1/+1
| | | | | | | | No functional changes.
* | tls: add Schannel implementationrfl8902025-08-071-0/+37
| | | | | | | | | | | | | | Not enabled by default. When enabled without TLS 1.3 support, saves 16784-18776 bytes. (GitHub PR #510)
* | stty: enable a minimal Windows implementationRon Yorston2025-07-251-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Implement a minimal stty applet for Windows. - Display and set terminal rows and columns - Enable/disable raw/cooked mode - Enable/disable echo mode - Implement 'stty sane' to reset raw/cooked/echo Adds 2120-2304 bytes. (GitHub issue #58)
* | win32: deduplicate die_if_error()Ron Yorston2025-07-111-0/+1
| | | | | | | | | | | | | | There were two copies of the static function die_if_error(). Replace these with a single external function. Saves 16 bytes.
* | format #definesRFL8902025-06-091-8/+8
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* | Use Windows library for cryptographic checksumscng_backendRon Yorston2025-06-091-0/+37
| | | | | | | | | | | | | | | | | | | | | | | | | | Add a new feature to libbb, FEATURE_USE_CNG_API, which enables the use of the Cryptography API: Next Generation library to calculate checksums. It is disabled by default except in the mingw64u default config, as the API requires Windows 10+ to function. Usage of this API provides a size benefit and delegates hardware optimizations to the operating system cryptography library. Based on GitHub PR #498 by rfl890. Saves 4064 bytes in the mingw64u case.
* | Merge branch 'busybox' into mergeRon Yorston2025-05-191-3/+3
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| * libbb/archival: make setup_unzip_on_fd() return bytes read if not compressedDenys Vlasenko2025-04-201-3/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | setup_unzip_on_fd() does not return the transformer structure, so the user does not know how much to seek back (or alternatively what the signature was) when compressor signature is not detected. Currently not needed (the only user is tar which dies anyway). However, rpm2cpio may need this if we extend it to extract the internal .cpio even if cpio's compressions algo is not known. function old new delta setup_unzip_on_fd 53 59 +6 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | win32: retry when command needs elevated privilegesRon Yorston2025-02-031-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Some installer programs have an entry in their manifest to indicate that they need elevated privileges. The shell in busybox-w32 was unable to run such programs. When a program fails to run with ERROR_ELEVATION_REQUIRED, try again using ShellExecuteEx() with the 'runas' verb to give it elevated privileges. Adds 272-288 bytes. (GitHub issue #481)
* | ash: match behaviour of cmd.exe in cd builtinRon Yorston2024-11-191-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | The Windows API strips trailing dots and spaces from the last component of a path. cmd.exe handles this quirk when changing directory by adjusting its idea of the current directory to match reality. The shell in busybox-w32 didn't do this, leading to some confusion. Fix the shell's cd builtin so it works more like cmd.exe. Adds 64-80 bytes. (GitHub issue #478)
* | test: code shrink supplementary groupsRon Yorston2024-10-091-0/+4
| | | | | | | | | | | | | | | | Since we don't use is_in_supplementary_groups() there's no need for the cached_groupinfo structure to include the members required for its support or for them to be initialised. Saves 32 bytes.
* | Merge branch 'busybox' into mergeRon Yorston2024-10-081-1/+1
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| * libbb: modify find_executable() to not temporarily write to PATHDenys Vlasenko2024-10-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | This allows to simplify "which" applet code function old new delta find_executable 93 111 +18 which_main 191 177 -14 builtin_source 316 294 -22 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/2 up/down: 18/-36) Total: -18 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | libbb: code shrink supplementary group testRon Yorston2024-10-081-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | Recent upstream changes to file permission tests added a function to check and cache values in the supplementary group list. The implementation of getgroups() in the Windows port adds no useful information beyond what can be obtained by checking the current effective gid, which all callers of the new function already do. The function can be replaced with a simple 'FALSE'. Saves 232-288 bytes.
* | Merge branch 'busybox' into mergeRon Yorston2024-10-081-0/+14
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| * ash: cache more of uid/gid syscallsDenys Vlasenko2024-10-071-2/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Testcase: setuidgid 1:1 strace ash -c 'test -x TODO; test -x TODO; echo $?' should show that second "test -x" does not query ids again. function old new delta ash_main 1236 1256 +20 get_cached_euid - 19 +19 get_cached_egid - 19 +19 test_main 56 72 +16 test_exec 119 135 +16 is_in_supplementary_groups 52 57 +5 nexpr 718 702 -16 ------------------------------------------------------------------------------ (add/remove: 2/0 grow/shrink: 4/1 up/down: 95/-16) Total: 79 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * ash: make "test -x" use cached groupinfoDenys Vlasenko2024-10-071-0/+1
| | | | | | | | | | | | | | | | | | | | | | function old new delta test_main2 - 407 +407 testcmd 10 23 +13 test_main 418 56 -362 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 1/1 up/down: 420/-362) Total: 58 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: simplify parameter passing in is_in_supplementary_groups()Denys Vlasenko2024-10-071-2/+8
| | | | | | | | | | | | | | | | | | | | | | function old new delta is_in_supplementary_groups 54 52 -2 nexpr 721 718 -3 test_exec 125 119 -6 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-11) Total: -11 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: move is_in_supplementary_groups() from test to libbbDenys Vlasenko2024-10-071-0/+5
| | | | | | | | | | | | | | | | | | | | function old new delta is_in_supplementary_groups - 54 +54 nexpr 766 721 -45 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 0/1 up/down: 54/-45) Total: 9 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | Merge branch 'busybox' into mergeRon Yorston2024-09-281-5/+5
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| * lineedit: make save_history() FAST_FUNCDenys Vlasenko2024-09-271-5/+5
| | | | | | | | | | | | | | | | | | | | | | function old new delta save_history 267 266 -1 hush_exit 98 97 -1 exitshell 140 138 -2 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-4) Total: -4 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | Use builtin ffs also with GCCChristopher Wellons2024-09-211-1/+1
| | | | | | | | | | | | | | | | With CONFIG_DEBUG_PESSIMIZE=y (-O0) the ffs intrinsic is left as a function call, resulting in a linker error. The prefixed builtin is generally part of the "GNU C" dialect and is usable in any "GNU C" implementation, i.e. any compiler that defines __GNUC__. That includes Clang, GCC, and more.
* | ash: optimise running of scripts (2)Ron Yorston2024-09-041-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 4b7b4a960 (ash: optimise running of scripts) avoided creation of a process when running a script. There's another case where we can do the same: if the script is being run from a FS_SHELLEXEC shell. - Check the necessary conditions for this to happen. - Allocate two extra slots in the argv array for FS_SHELLEXEC. - Set the index of the script file in the argv array. Without this the test 'pidof this' failed because the command name hadn't been correctly set. Adds 80-96 bytes.
* | ash: optimise running of scriptsRon Yorston2024-08-191-0/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The BusyBox shell detects certain cases where forking a command is unnecessary (last command in a script or subshell, for example) and calls execve(2) instead. This doesn't help in the Windows port because execve(2) is implemented by creating a process. There is one case where it is possible to apply this optimisation: if the command is a script and the script interpreter is an applet. - Have evalcommand() pass a flag to indicate this situation to shellexec(). Also, allocate two spare elements before the start of the argv array. - If the flag is TRUE shellexec() passes the shell's PATH variable down to tryexec() so it can perform a test for applet override. - If tryexec() finds that all the necessary conditions apply it can run a script by directly invoking the interpreter's main(). Adds 192-224 bytes.
* | win32: code shrinkRon Yorston2024-08-161-17/+17
| | | | | | | | | | Add the FAST_FUNC qualifier to several Windows-specific functions. This has no effect in 64-bit builds but saves 336 bytes for 32-bit.
* | win32: use 64-bit time on 32-bit platformsRon Yorston2024-08-142-0/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | To avoid problems with dates in 2038 and beyond use 64-bit time values on 32-bit platforms. - Mostly this just requires a few preprocessor macros to choose the appropriate functions, structs and typedefs. - We have our own implementations of nanosleep(), clock_gettime() and clock_settime(). Omit the Windows include file that declares them. - Apply the hack for struct timeval in the 'ts' applet on 32-bit. Adds 1624 bytes on 32-bit, none on 64-bit. (GitHub issue #446)
* | su: detect inability to raise privilegeRon Yorston2024-08-031-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | When privilege has been dropped by the 'drop' applet, the 'su' applet is unable to raise it again because ShellExecuteEx() thinks it unnecessary. Detect this situation, report an error and return exit code 2. Costs 72-112 bytes. (GitHub issue #437)
* | ash: read profile script relative to binaryRon Yorston2024-07-081-0/+1
| | | | | | | | | | | | | | As well as trying to read '/etc/profile' also look for the script 'etc/profile' relative to the location of the running binary. Adds 64-96 bytes.
* | win32: code shrink system drive handlingRon Yorston2024-07-071-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | A previous commit (e3bfe3695) revised the use of getsysdir() to obtain the system directory, and hence the system drive. See the commit message for the history to that point. Further improvements are possible: - Remove getsysdir() and push the calls to GetSystemDirectory() down into get_system_drive() and get_proc_addr(). - Check the return value of GetSystemDirectory(). It's unlikely to fail, but better safe than sorry. - Instead of making all callers of get_system_drive() check for a NULL return value always return a non-NULL pointer. If the drive can't be found an empty string is returned instead (which is what the callers were using anyway). - The function need_system_drive() was only used in one place (in httpd). Move the code there and remove the function. - Use concat_path_file() where possible. Saves 76-144 bytes.
* | Merge branch 'busybox' into mergeRon Yorston2024-06-231-0/+9
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| * libbb: fix 64-bit bb_popcnt_longDenys Vlasenko2024-05-311-1/+1
| | | | | | | | Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * libbb: add bit counting function, use where appropriateDenys Vlasenko2024-05-311-0/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Although "naive" counting function is not too slow and is smaller, using it on e.g. each of 1024 words of CPU mask feels wrong. function old new delta bb_popcnt_32 - 52 +52 get_prefix 323 321 -2 nproc_main 206 199 -7 d4_run_script 739 731 -8 ipcalc_main 533 507 -26 ------------------------------------------------------------------------------ (add/remove: 2/0 grow/shrink: 0/4 up/down: 52/-43) Total: 9 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| * nproc: prepare for arbitrarily large CPU masksDenys Vlasenko2024-05-311-0/+2
| | | | | | | | | | | | | | | | | | | | | | function old new delta get_malloc_cpu_affinity - 76 +76 nproc_main 216 206 -10 process_pid_str 250 206 -44 ------------------------------------------------------------------------------ (add/remove: 2/0 grow/shrink: 0/2 up/down: 76/-54) Total: 22 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
* | win32: add env var to control error dialogsRon Yorston2024-06-222-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If the environment variable BB_CRITICAL_ERROR_DIALOGS is set to 1 critical error dialogs are enabled. If unset or set to any other value they aren't. In either case the error messages introduced by commit 790e37727 (win32: revert 'don't set error mode') are issued. The shell exports BB_CRITICAL_ERROR_DIALOGS to the environment immediately on any change so the setting takes effect at once. Adds 104-160 bytes. (GitHub issue #423)
* | win32: allow for trailing separator in PATHRon Yorston2024-06-141-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In recent versions of Windows the PATH environment variable has a trailing semicolon. This is insignificant to Windows because it's ignored. busybox-w32 conforms to the POSIX interpretation of PATH which treats an empty path element as denoting the current directory. As result, on these versions of Windows executables may by default be run from the current directory, contrary to usual Unix practice. Attempt to detect and remove the trailing semicolon on applet start up. If the user insists, they can add a trailing semicolon to the shell variable PATH and it will be respected in the conventional manner. Adds 88-112 bytes. (GitHub issue #422)
* | win32: implement getppid(2)Ron Yorston2024-05-161-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | busybox-w32 had a dummy implementation of getppid(2) which always returned 1. Provide a more realistic version. The effect is limited: - The PPID shell variable should report a sensible value. - The special value to omit the parent PID 'pidof -o %PPID' should work. Costs 48 bytes.
* | win32: ensure PIDs are read early in procps_scan()Ron Yorston2024-05-161-2/+1
| | | | | | | | | | | | | | | | | | | | | | Recent changes to allow orphaned processes to report a parent PID of 1 rely on the assumption that Process32First/Process32Next return parents before children. This isn't guaranteed by the API. Obtain all known PIDs on the first call to procps_scan() so that dead parents can be detected reliably. Costs 48 bytes.
* | ps: report unknown parent PID as 1Ron Yorston2024-05-141-0/+3
| | | | | | | | | | | | | | | | | | | | If the parent PID doesn't appear in the process table, report it as 1. This more closely matches how orphaned children are handled on UNIX. Adds 96-128 bytes. (GitHub issue #416)
* | kill: killing a zombie process should failRon Yorston2024-05-141-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | A process which has exited may still have its process handle held open by its children. Such a process doesn't appear in the process table. It is thus similar to a zombie process in UNIX. Using kill(1) to interact with such a process was seen to succeed, contrary to expectation. The code for "ordinary" signals in kill(2) did check if the process was still active but didn't treat an attempt to kill an inactive process as an error. Furthermore, sending SIGKILL or the fake signal 0 to a process didn't even check if the process was still active. Rearrange the implementation of kill(2) so that an attempt to signal an inactive process is treated as an error. This also consolidates handling of SIGKILL and signal 0 with "ordinary" signals. Saves 96 bytes. (GitHub issue #416)