[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #11 from Andrew Pinski --- (In reply to piliu from comment #10) > (In reply to Andrew Pinski from comment #7) > > I am trying to understand this. Is it ok to use the SSE registers inside > > purgatory or not? > > > > SSE can speed up the program, and if possible it is suggested to turn on. > > Any guideline about when it can not be used? Yes if you are inside the kernel/bootloader SSE might not be turned on. So my question here. Normal parts of the kernel cannot use SSE instructions either which is why there is an option to turn it off. Maybe it is best to ask the kexec-tools folks if SSE can be used here. I suspect you cannot. GCC was not emitting SSE instructions before and now is at -O2 which is why -fno-tree-vectorize works as it turns off emitting of SSE instructions again. There is nothing wrong with what GCC emits for sha256_starts for the options kexec-tools supplied even, just it is supplying the wrong set of options in the first place. For user code SSE code is always fine as the compiler and glibc has been using SSE code early on. As I said it if it is a bootloader/kernel, then you have to ask is SSE turned on or not and do we save/restore the registers correctly, etc.
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #10 from piliu at redhat dot com --- (In reply to Andrew Pinski from comment #7) > I am trying to understand this. Is it ok to use the SSE registers inside > purgatory or not? > SSE can speed up the program, and if possible it is suggested to turn on. Any guideline about when it can not be used? > Now that the vectorizer is used turned on at -O2 and above, without > -mno-sse, on x86_64 target, the vector instructions are generated. and since > this is inside a tiny bootloader, I am suspecting you can't use SSE > instructions here. > What is broken by SSE? That can be more persuaded. Thanks, Pingfan
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #9 from Andrew Pinski --- https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/commit/purgatory/Makefile?id=1b03cf7adc3c156ecab2618acb1ec585336a3f75 was the commit to "fix" this but as I think I mentioned here it is just a workaround for expecting SSE code to work and GCC might emit SSE code in other places without the autovectorizer enabled so
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #8 from Andrew Pinski --- Looks like only ppc64 does: ppc64_PURGATORY_EXTRA_CFLAGS += -m64 -msoft-float \ -fno-exceptions Most likely purgatory/arch/x86_64/Makefile needs the following added the end of the file instead: x86_64_PURGATORY_EXTRA_CFLAGS += -mno-sse (-mgeneral-regs-only might work these days too) purgatory/arch/arm64/Makefile needs the following added too: arm64_PURGATORY_EXTRA_CFLAGS += -mgeneral-regs-only Other targets might need other CFLAGS set here for the same reason.
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #7 from Andrew Pinski --- I am trying to understand this. Is it ok to use the SSE registers inside purgatory or not? Now that the vectorizer is used turned on at -O2 and above, without -mno-sse, on x86_64 target, the vector instructions are generated. and since this is inside a tiny bootloader, I am suspecting you can't use SSE instructions here. So the real fix is to use -mno-sse for x86_64 while compiling files under purgatory .
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #6 from piliu at redhat dot com --- Created attachment 52757 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52757=edit precompiled code of sha256 compile command: gcc -E -fno-zero-initialized-in-bss -mcmodel=large -Os -fno-builtin -ffreestanding -fno-zero-initialized-in-bss -fno-PIC -fno-PIE -fno-stack-protector -O2 -mcmodel=large -I./purgatory/include -I./purgatory/arch/x86_64/include -I./util_lib/include -I./include -Iinclude -I/usr/lib/gcc/x86_64-redhat-linux/12/include -c -o purgatory/sha256.o util_lib/sha256.c
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #5 from piliu at redhat dot com --- Created attachment 52756 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52756=edit -ftree-vectorize can not produce correct code for kexec-tools
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 --- Comment #4 from piliu at redhat dot com --- (In reply to Richard Biener from comment #3) > Can you provide preprocessed source of the TU containing sha256_starts and > the full compiler command-line used to compile it? For a single file. gcc -fno-zero-initialized-in-bss -mcmodel=large -Os -fno-builtin -ffreestanding -fno-zero-initialized-in-bss -fno-PIC -fno-PIE -fno-stack-protector -O2 -mcmodel=large -I./purgatory/include -I./purgatory/arch/x86_64/include -I./util_lib/include -I./include -Iinclude -I/usr/lib/gcc/x86_64-redhat-linux/12/include -c -o purgatory/sha256.o util_lib/sha256.c For the complete compile log, please see the attachment.
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134 Richard Biener changed: What|Removed |Added Last reconfirmed||2022-04-04 Ever confirmed|0 |1 Status|UNCONFIRMED |WAITING --- Comment #3 from Richard Biener --- Can you provide preprocessed source of the TU containing sha256_starts and the full compiler command-line used to compile it?
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134
--- Comment #2 from piliu at redhat dot com ---
More specific, the following directive beats out the bug.
diff --git a/util_lib/sha256.c b/util_lib/sha256.c
index 2e61a31..3b3e533 100644
--- a/util_lib/sha256.c
+++ b/util_lib/sha256.c
@@ -38,6 +38,7 @@
(b)[(i) + 3] = (uint8_t) ( (n) ); \
}
+ __attribute__((optimize("no-tree-vectorize")))
void sha256_starts( sha256_context *ctx )
[Bug c/105134] tree-vectorize produces error code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105134
--- Comment #1 from piliu at redhat dot com ---
More description about the background.
There is a built file kexec-tools/purgatory/purgatory.ro, which is a tiny
bootload, compare and verify the sha256, if ok, then jump to the 2nd kernel.
The original sha256 value comes from
update_purgatory()
{
..
elf_rel_set_symbol(>rhdr, "sha256_regions", ,
sizeof(region));
elf_rel_set_symbol(>rhdr, "sha256_digest", ,
sizeof(digest));
}
They are based on the loaded linux kernel image.
Now, "kexec -e" and purgatory.ro runs, and in
void purgatory(void)
{
printf("I'm in purgatory\n");
setup_arch();
if (!skip_checks && verify_sha256_digest()) {
for(;;) {
/* loop forever */ --> stuck here
}
}
post_verification_setup_arch();
}
