mirror of
https://github.com/torvalds/linux.git
synced 2024-11-22 04:38:03 +00:00
4356e9f841
We've had issues with gcc and 'asm goto' before, and we created a 'asm_volatile_goto()' macro for that in the past: see commits3f0116c323("compiler/gcc4: Add quirk for 'asm goto' miscompilation bug") anda9f180345f("compiler/gcc4: Make quirk for asm_volatile_goto() unconditional"). Then, much later, we ended up removing the workaround in commit43c249ea0b("compiler-gcc.h: remove ancient workaround for gcc PR 58670") because we no longer supported building the kernel with the affected gcc versions, but we left the macro uses around. Now, Sean Christopherson reports a new version of a very similar problem, which is fixed by re-applying that ancient workaround. But the problem in question is limited to only the 'asm goto with outputs' cases, so instead of re-introducing the old workaround as-is, let's rename and limit the workaround to just that much less common case. It looks like there are at least two separate issues that all hit in this area: (a) some versions of gcc don't mark the asm goto as 'volatile' when it has outputs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420 which is easy to work around by just adding the 'volatile' by hand. (b) Internal compiler errors: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422 which are worked around by adding the extra empty 'asm' as a barrier, as in the original workaround. but the problem Sean sees may be a third thing since it involves bad code generation (not an ICE) even with the manually added 'volatile'. but the same old workaround works for this case, even if this feels a bit like voodoo programming and may only be hiding the issue. Reported-and-tested-by: Sean Christopherson <seanjc@google.com> Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/ Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Uros Bizjak <ubizjak@gmail.com> Cc: Jakub Jelinek <jakub@redhat.com> Cc: Andrew Pinski <quic_apinski@quicinc.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
66 lines
1.6 KiB
C
66 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
/* Copyright (C) 2018 Cadence Design Systems Inc. */
|
|
|
|
#ifndef _ASM_XTENSA_JUMP_LABEL_H
|
|
#define _ASM_XTENSA_JUMP_LABEL_H
|
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
#include <linux/types.h>
|
|
|
|
#define JUMP_LABEL_NOP_SIZE 3
|
|
|
|
static __always_inline bool arch_static_branch(struct static_key *key,
|
|
bool branch)
|
|
{
|
|
asm goto("1:\n\t"
|
|
"_nop\n\t"
|
|
".pushsection __jump_table, \"aw\"\n\t"
|
|
".word 1b, %l[l_yes], %c0\n\t"
|
|
".popsection\n\t"
|
|
: : "i" (&((char *)key)[branch]) : : l_yes);
|
|
|
|
return false;
|
|
l_yes:
|
|
return true;
|
|
}
|
|
|
|
static __always_inline bool arch_static_branch_jump(struct static_key *key,
|
|
bool branch)
|
|
{
|
|
/*
|
|
* Xtensa assembler will mark certain points in the code
|
|
* as unreachable, so that later assembler or linker relaxation
|
|
* passes could use them. A spot right after the J instruction
|
|
* is one such point. Assembler and/or linker may insert padding
|
|
* or literals here, breaking code flow in case the J instruction
|
|
* is later replaced with NOP. Put a label right after the J to
|
|
* make it reachable and wrap both into a no-transform block
|
|
* to avoid any assembler interference with this.
|
|
*/
|
|
asm goto("1:\n\t"
|
|
".begin no-transform\n\t"
|
|
"_j %l[l_yes]\n\t"
|
|
"2:\n\t"
|
|
".end no-transform\n\t"
|
|
".pushsection __jump_table, \"aw\"\n\t"
|
|
".word 1b, %l[l_yes], %c0\n\t"
|
|
".popsection\n\t"
|
|
: : "i" (&((char *)key)[branch]) : : l_yes);
|
|
|
|
return false;
|
|
l_yes:
|
|
return true;
|
|
}
|
|
|
|
typedef u32 jump_label_t;
|
|
|
|
struct jump_entry {
|
|
jump_label_t code;
|
|
jump_label_t target;
|
|
jump_label_t key;
|
|
};
|
|
|
|
#endif /* __ASSEMBLY__ */
|
|
#endif
|