build system: make CONFIG_FEATURE_USE_BSS_TAIL less funky

CONFIG_FEATURE_USE_BSS_TAIL code was aliasing bb_common_bufsiz1 to _end.
This is unreliable: _end may be not sufficiently aligned.

Change code to simply enlarge COMMON_BUFSIZE when we detect that _end
has significant amount of space to the end of page.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 28 insertions, 72 deletions

diff --git a/scripts/generate_BUFSIZ.sh b/scripts/generate_BUFSIZ.sh
index 844261906..718788e0b 100755
--- a/scripts/generate_BUFSIZ.sh
+++ b/scripts/generate_BUFSIZ.sh
@@ -36,11 +36,10 @@ generate_std_and_exit() {
 }
 
 generate_big_and_exit() {
-        $debug && echo "Configuring: bb_common_bufsiz1[] in _end[], COMMON_BUFSIZE = $1"
+        $debug && echo "Configuring: bb_common_bufsiz1[] in bss, COMMON_BUFSIZE = $1"
         {
         echo "enum { COMMON_BUFSIZE = $1 };"
-        echo "extern char _end[]; /* linker-provided label */"
-        echo "#define bb_common_bufsiz1 _end"
+        echo "extern char bb_common_bufsiz1[];"
         echo "#define setup_common_bufsiz() ((void)0)"
         } | regenerate "$common_bufsiz_h"
         echo "$2" >"$common_bufsiz_h.method"
@@ -51,20 +50,10 @@ generate_1k_and_exit() {
         generate_big_and_exit 1024 "1k"
 }
 
-
-generate_malloc_and_exit() {
-        $debug && echo "Configuring: bb_common_bufsiz1[] is malloced"
-        {
-        echo "enum { COMMON_BUFSIZE = 1024 };"
-        echo "extern char *const bb_common_bufsiz1;"
-        echo "void setup_common_bufsiz(void);"
-        } | regenerate "$common_bufsiz_h"
-        echo "malloc" >"$common_bufsiz_h.method"
-        $exitcmd
-}
-
 round_down_COMMON_BUFSIZE() {
-        COMMON_BUFSIZE=$(( ($1-32) & 0xfffffe0 ))
+        COMMON_BUFSIZE=1024
+        test "$1" -le 32 && return
+        COMMON_BUFSIZE=$(( ($1-32) & 0x0ffffff0 ))
         COMMON_BUFSIZE=$(( COMMON_BUFSIZE < 1024 ? 1024 : COMMON_BUFSIZE ))
 }
 
@@ -104,77 +93,44 @@ if $postcompile; then
         test x"$PAGE_SIZE" = x"" && exit 1
         $debug && echo "PAGE_SIZE:0x$PAGE_SIZE $((0x$PAGE_SIZE))"
         PAGE_SIZE=$((0x$PAGE_SIZE))
-        test $PAGE_SIZE -lt 512 && exit 1
+        test $PAGE_SIZE -lt 1024 && exit 1
 
         # How much space between _end[] and next page?
         PAGE_MASK=$((PAGE_SIZE-1))
         TAIL_SIZE=$(( (-END) & PAGE_MASK ))
         $debug && echo "TAIL_SIZE:$TAIL_SIZE bytes"
 
-        if test x"$method" = x"1k" || test x"$method" = x"big"; then
-                if test $TAIL_SIZE -lt 1024; then
-                        # _end[] has no enough space for bb_common_bufsiz1[]
-                        echo "Warning! Space in _end[] is too small ($TAIL_SIZE bytes)!"
-                        echo "Rerun make to build a binary which doesn't use it!"
-                        rm -- "$common_bufsiz_h.1k.OK" 2>/dev/null
-                        { md5sum <.config | cut -d' ' -f1; stat -c "%Y" .config; } >"$common_bufsiz_h.1k.FAIL"
-                        rm busybox_unstripped busybox 2>/dev/null
-# Note: here we can do either a "malloc" or "std" build.
-# "malloc" gives a bit bigger code:
-#     text  bss filename
-#   804355 5385 busybox.std
-#   804618 4361 busybox.malloc
-# but may have a smaller .bss (not guaranteed!). Use "pmap -x" to verify.
-                        exitcmd="exit 1"
-                        generate_malloc_and_exit
-                else
-                        PREV_SIZE=1024
-                        test x"$method" = x"big" && PREV_SIZE=`cat -- "$common_bufsiz_h.1k.OK"`
-                        round_down_COMMON_BUFSIZE $PREV_SIZE
-                        PREV_BUFSIZE=$COMMON_BUFSIZE
-
-                        rm -- "$common_bufsiz_h.1k.FAIL" 2>/dev/null
-                        echo $TAIL_SIZE >"$common_bufsiz_h.1k.OK"
-                        round_down_COMMON_BUFSIZE $TAIL_SIZE
-                        # emit message only if COMMON_BUFSIZE is indeed larger
-                        test $COMMON_BUFSIZE -gt $PREV_BUFSIZE \
-                                && echo "Rerun make to use larger COMMON_BUFSIZE ($COMMON_BUFSIZE)"
-#TODO: test $PREV_BUFSIZE -lt $TAIL_SIZE && PANIC!!!
-#Code size with COMMON_BUFSIZE > 1024 may be bigger than code with COMMON_BUFSIZE = 1024!
-#(currently we just hope "-32 and round down to 32" saves us)
-
-                        test $COMMON_BUFSIZE = 1024 && generate_1k_and_exit
-                        generate_big_and_exit $COMMON_BUFSIZE "big"
-                fi
+        if test x"$method" = x"1k"; then
+                {
+                echo $TAIL_SIZE
+                md5sum <.config | cut -d' ' -f1
+                stat -c "%Y" .config
+                } >"$common_bufsiz_h.1k.OK"
+                round_down_COMMON_BUFSIZE $((1024 + TAIL_SIZE))
+                # emit message only if COMMON_BUFSIZE is indeed larger
+                test $COMMON_BUFSIZE -gt 1024 \
+                        && echo "Rerun make to use larger COMMON_BUFSIZE ($COMMON_BUFSIZE)"
+                test $COMMON_BUFSIZE = 1024 && generate_1k_and_exit
+                generate_big_and_exit $COMMON_BUFSIZE "big"
         fi
 fi
 
 # Based on past success/fail of 1k build, decide next build type
 
 if test -f "$common_bufsiz_h.1k.OK"; then
-        # Previous build succeeded fitting 1k into _end[].
-        # Try bigger COMMON_BUFSIZE if possible.
-        TAIL_SIZE=`cat -- "$common_bufsiz_h.1k.OK"`
-        round_down_COMMON_BUFSIZE $TAIL_SIZE
-        test $COMMON_BUFSIZE = 1024 && generate_1k_and_exit
-        generate_big_and_exit $COMMON_BUFSIZE "big"
-fi
-
-if test -f "$common_bufsiz_h.1k.FAIL"; then
-        # Previous build FAILED to fit 1k into _end[].
-        # Was it with same .config?
-        oldcfg=`cat -- "$common_bufsiz_h.1k.FAIL"`
+        # previous 1k build succeeded
+        oldcfg=`tail -n2 -- "$common_bufsiz_h.1k.OK"`
         curcfg=`md5sum <.config | cut -d' ' -f1; stat -c "%Y" .config`
-        # If yes, then build a "malloced" version
+        # config did not change
         if test x"$oldcfg" = x"$curcfg"; then
-                echo "Will not try 1k build, it failed before. Touch .config to override"
-# Note: here we can do either a "malloc" or "std" build.
-                generate_malloc_and_exit
+                # Try bigger COMMON_BUFSIZE if possible
+                TAIL_SIZE=`head -n1 -- "$common_bufsiz_h.1k.OK"`
+                round_down_COMMON_BUFSIZE $((1024 + TAIL_SIZE))
+                test $COMMON_BUFSIZE = 1024 && generate_1k_and_exit
+                generate_big_and_exit $COMMON_BUFSIZE "big"
         fi
-        # else: try 1k version
-        echo "New .config, will try 1k build"
-        rm -- "$common_bufsiz_h.1k.FAIL"
-        generate_1k_and_exit
+        # config did change
+        rm -rf -- "$common_bufsiz_h.1k.OK"
 fi
 
 # There was no 1k build yet. Try it.