ash: cache more of uid/gid syscalls

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>

1 files changed, 5 insertions, 4 deletions

diff --git a/shell/ash.c b/shell/ash.c
index a6bb9894c..9173b8608 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -536,6 +536,8 @@ extern struct globals_misc *BB_GLOBAL_CONST ash_ptr_to_globals_misc;
         curdir = nullstr; \
         physdir = nullstr; \
         trap_ptr = trap; \
+        groupinfo.euid = -1; \
+        groupinfo.egid = -1; \
 } while (0)
 
 
@@ -2319,7 +2321,7 @@ initvar(void)
 #if ENABLE_FEATURE_EDITING && ENABLE_FEATURE_EDITING_FANCY_PROMPT
         vps1.var_text = "PS1=\\w \\$ ";
 #else
-        if (!geteuid())
+        if (!get_cached_euid(&groupinfo.euid));
                 vps1.var_text = "PS1=# ";
 #endif
         vp = varinit;
@@ -13809,14 +13811,13 @@ static int test_exec(/*const char *fullname,*/ struct stat *statb)
 
         /* Executability depends on our euid/egid/supplementary groups */
         stmode = S_IXOTH;
-        euid = geteuid();
-//TODO: cache euid?
+        euid = get_cached_euid(&groupinfo.euid);
         if (euid == 0)
                 /* for root user, any X bit is good enough */
                 stmode = ANY_IX;
         else if (statb->st_uid == euid)
                 stmode = S_IXUSR;
-        else if (statb->st_gid == getegid())
+        else if (statb->st_gid == get_cached_egid(&groupinfo.egid))
                 stmode = S_IXGRP;
         else if (is_in_supplementary_groups(&groupinfo, statb->st_gid))
                 stmode = S_IXGRP;