x86: bug.h: use asm_inline in _BUG_FLAGS definitions

This helps preventing a BUG* or WARN* in some static inline from
preventing that (or one of its callers) being inlined, so should allow
gcc to make better informed inlining decisions.

For example, with gcc 9.2, tcp_fastopen_no_cookie() vanishes from
net/ipv4/tcp_fastopen.o. It does not itself have any BUG or WARN, but
it calls dst_metric() which has a WARN_ON_ONCE - and despite that
WARN_ON_ONCE vanishing since the condition is compile-time false,
dst_metric() is apparently sufficiently "large" that when it gets
inlined into tcp_fastopen_no_cookie(), the latter becomes too large
for inlining.

Overall, if one asks size(1), .text decreases a little and .data
increases by about the same amount (x86-64 defconfig)

$ size vmlinux.{before,after}
   text    data     bss     dec     hex filename
19709726        5202600 1630280 26542606        195020e vmlinux.before
19709330        5203068 1630280 26542678        1950256 vmlinux.after

while bloat-o-meter says

add/remove: 10/28 grow/shrink: 103/51 up/down: 3669/-2854 (815)
...
Total: Before=14783683, After=14784498, chg +0.01%

Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 6804d66..facba9b 100644 (file)
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -32,7 +32,7 @@
 
 #define _BUG_FLAGS(ins, flags)                                         \
 do {                                                                   \
-       asm volatile("1:\t" ins "\n"                                    \
+       asm_inline volatile("1:\t" ins "\n"                             \
                     ".pushsection __bug_table,\"aw\"\n"                \
                     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"   \
                     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"       \
@@ -49,7 +49,7 @@ do {                                                                  \
 
 #define _BUG_FLAGS(ins, flags)                                         \
 do {                                                                   \
-       asm volatile("1:\t" ins "\n"                                    \
+       asm_inline volatile("1:\t" ins "\n"                             \
                     ".pushsection __bug_table,\"aw\"\n"                \
                     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"   \
                     "\t.word %c0"        "\t# bug_entry::flags\n"      \