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authorJosh Poimboeuf <jpoimboe@redhat.com>2016-03-02 18:39:36 -0600
committerIngo Molnar <mingo@kernel.org>2016-03-03 16:13:00 +0100
commit19072f23d1d785c093b7f81cb1fb161e7a13ecc0 (patch)
tree11c60926a8f7a5873d33147a108f2d4e7c5f968e /arch/x86
parentd4883d5d6b146fd65f762c462b2c6d4a327c7d50 (diff)
downloadlinux-19072f23d1d785c093b7f81cb1fb161e7a13ecc0.tar.bz2
x86/asm/decoder: Use explicitly signed chars
When running objtool on a ppc64le host to analyze x86 binaries, it reports a lot of false warnings like: ipc/compat_mq.o: warning: objtool: compat_SyS_mq_open()+0x91: can't find jump dest instruction at .text+0x3a5 The warnings are caused by the x86 instruction decoder setting the wrong value for the jump instruction's immediate field because it assumes that "char == signed char", which isn't true for all architectures. When converting char to int, gcc sign-extends on x86 but doesn't sign-extend on ppc64le. According to the gcc man page, that's a feature, not a bug: > Each kind of machine has a default for what "char" should be. It is > either like "unsigned char" by default or like "signed char" by > default. > > Ideally, a portable program should always use "signed char" or > "unsigned char" when it depends on the signedness of an object. Conform to the "standards" by changing the "char" casts to "signed char". This results in no actual changes to the object code on x86. Note: the x86 decoder now lives in three different locations in the kernel tree, which are all kept in sync via makefile checks and warnings: in-kernel, perf, and objtool. This fixes all three locations. Eventually we should probably try to at least converge the two separate "tools" locations into a single shared location. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/9dd4161719b20e6def9564646d68bfbe498c549f.1456962210.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/lib/insn.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 8f72b334aea0..1a416935bac9 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -374,7 +374,7 @@ void insn_get_displacement(struct insn *insn)
if (mod == 3)
goto out;
if (mod == 1) {
- insn->displacement.value = get_next(char, insn);
+ insn->displacement.value = get_next(signed char, insn);
insn->displacement.nbytes = 1;
} else if (insn->addr_bytes == 2) {
if ((mod == 0 && rm == 6) || mod == 2) {
@@ -532,7 +532,7 @@ void insn_get_immediate(struct insn *insn)
switch (inat_immediate_size(insn->attr)) {
case INAT_IMM_BYTE:
- insn->immediate.value = get_next(char, insn);
+ insn->immediate.value = get_next(signed char, insn);
insn->immediate.nbytes = 1;
break;
case INAT_IMM_WORD:
@@ -566,7 +566,7 @@ void insn_get_immediate(struct insn *insn)
goto err_out;
}
if (inat_has_second_immediate(insn->attr)) {
- insn->immediate2.value = get_next(char, insn);
+ insn->immediate2.value = get_next(signed char, insn);
insn->immediate2.nbytes = 1;
}
done: