https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84861
Bug ID: 84861
Summary: -flto with asm() optimizes too much
Product: gcc
Version: lto
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
Assignee: unassigned at gcc dot gnu.org
Reporter: dilyan.palauzov at aegee dot org
Target Milestone: ---
When compiling valgrind's coregrind/m_libcsetjmp.c
(https://sourceware.org/git/?p=valgrind.git;a=blob;f=coregrind/m_libcsetjmp.c)
with -lto the functions VG_MINIMAL_LONGJMP and VG_MINIMAL_SETJMP disappear on
amd64 from the coregrind/libcoregrind_amd64_linux_a-m_libcsetjmp.o file:
cd coregrind
WITH LTO:
$ make V=1 libcoregrind_amd64_linux_a-m_libcsetjmp.o
gcc -DHAVE_CONFIG_H -I. -I.. -I.. -I../include -I../include -I../VEX/pub
-I../VEX/pub -DVGA_amd64=1 -DVGO_linux=1 -DVGP_amd64_linux=1
-DVGPV_amd64_linux_vanilla=1 -I../coregrind
-DVG_LIBDIR="\"/usr/local/lib/valgrind"\" -DVG_PLATFORM="\"amd64-linux\"" -m64
-O2 -finline-functions -g -Wall -Wmissing-prototypes -Wshadow -Wpointer-arith
-Wstrict-prototypes -Wmissing-declarations -Wcast-align -Wcast-qual
-Wwrite-strings -Wempty-body -Wformat -Wformat-security -Wignored-qualifiers
-Wmissing-parameter-type -Wlogical-op -Wold-style-declaration
-fno-stack-protector -fno-strict-aliasing -fno-builtin -fomit-frame-pointer
-DENABLE_LINUX_TICKET_LOCK -flto -MT libcoregrind_amd64_linux_a-m_libcsetjmp.o
-MD -MP -MF .deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Tpo -c -o
libcoregrind_amd64_linux_a-m_libcsetjmp.o `test -f 'm_libcsetjmp.c' || echo
'./'`m_libcsetjmp.c
mv -f .deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Tpo
.deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Po
$ nm libcoregrind_amd64_linux_a-m_libcsetjmp.o
nm: libcoregrind_amd64_linux_a-m_libcsetjmp.o: no symbols
(for the other coregrind/libcoregrind_amd64_linux_a-*.o files `nm` shows
exported symbols).
WITHOUT LTO:
$ make V=1 libcoregrind_amd64_linux_a-m_libcsetjmp.o
gcc -DHAVE_CONFIG_H -I. -I.. -I.. -I../include -I../include -I../VEX/pub
-I../VEX/pub -DVGA_amd64=1 -DVGO_linux=1 -DVGP_amd64_linux=1
-DVGPV_amd64_linux_vanilla=1 -I../coregrind
-DVG_LIBDIR="\"/usr/local/lib/valgrind"\" -DVG_PLATFORM="\"amd64-linux\"" -m64
-O2 -finline-functions -g -Wall -Wmissing-prototypes -Wshadow -Wpointer-arith
-Wstrict-prototypes -Wmissing-declarations -Wcast-align -Wcast-qual
-Wwrite-strings -Wempty-body -Wformat -Wformat-security -Wignored-qualifiers
-Wmissing-parameter-type -Wlogical-op -Wold-style-declaration
-fno-stack-protector -fno-strict-aliasing -fno-builtin -fomit-frame-pointer
-DENABLE_LINUX_TICKET_LOCK -MT libcoregrind_amd64_linux_a-m_libcsetjmp.o
-MD -MP -MF .deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Tpo -c -o
libcoregrind_amd64_linux_a-m_libcsetjmp.o `test -f 'm_libcsetjmp.c' || echo
'./'`m_libcsetjmp.c
mv -f .deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Tpo
.deps/libcoregrind_amd64_linux_a-m_libcsetjmp.Po
$ nm libcoregrind_amd64_linux_a-m_libcsetjmp.o
0000000000000052 T VG_MINIMAL_LONGJMP
0000000000000000 T VG_MINIMAL_SETJMP
The only difference is "-flto".
It this a problem of LTO, or is the assembler supposed to be tweaked (how?) so
that the symbols get exported?
Having a file containing
asm ("");
does compile, but a file containing only:
asm volatile ("");
fails with "error: expected ‘(’ before ‘volatile’".
Happens with gcc 8.0.1 20180306 (experimental).
