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Date: Thu, 03 Mar 2016 11:00:26 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: linux-tip-commits@...r.kernel.org,
tip-bot for Josh Poimboeuf <tipbot@...or.com>
CC: mingo@...nel.org, sfr@...b.auug.org.au,
linux-kernel@...r.kernel.org, tglx@...utronix.de,
mpe@...erman.id.au, masami.hiramatsu.pt@...achi.com,
adrian.hunter@...el.com, jpoimboe@...hat.com,
torvalds@...ux-foundation.org, peterz@...radead.org
Subject: Re: [tip:core/objtool] x86/asm/decoder: Use explicitly signed chars
On March 3, 2016 8:51:39 AM PST, tip-bot for Josh Poimboeuf <tipbot@...or.com> wrote:
>Commit-ID: 19072f23d1d785c093b7f81cb1fb161e7a13ecc0
>Gitweb:
>http://git.kernel.org/tip/19072f23d1d785c093b7f81cb1fb161e7a13ecc0
>Author: Josh Poimboeuf <jpoimboe@...hat.com>
>AuthorDate: Wed, 2 Mar 2016 18:39:36 -0600
>Committer: Ingo Molnar <mingo@...nel.org>
>CommitDate: Thu, 3 Mar 2016 16:13:00 +0100
>
>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@...hat.com>
>Cc: Adrian Hunter <adrian.hunter@...el.com>
>Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>Cc: Michael Ellerman <mpe@...erman.id.au>
>Cc: Peter Zijlstra <peterz@...radead.org>
>Cc: Stephen Rothwell <sfr@...b.auug.org.au>
>Cc: Thomas Gleixner <tglx@...utronix.de>
>Link:
>http://lkml.kernel.org/r/9dd4161719b20e6def9564646d68bfbe498c549f.1456962210.git.jpoimboe@redhat.com
>Signed-off-by: Ingo Molnar <mingo@...nel.org>
>---
> arch/x86/lib/insn.c | 6 +++---
> tools/objtool/arch/x86/insn/insn.c | 6 +++---
> tools/perf/util/intel-pt-decoder/insn.c | 6 +++---
> 3 files changed, 9 insertions(+), 9 deletions(-)
>
>diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
>index 8f72b33..1a41693 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:
>diff --git a/tools/objtool/arch/x86/insn/insn.c
>b/tools/objtool/arch/x86/insn/insn.c
>index 47314a6..9f26eae 100644
>--- a/tools/objtool/arch/x86/insn/insn.c
>+++ b/tools/objtool/arch/x86/insn/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:
>diff --git a/tools/perf/util/intel-pt-decoder/insn.c
>b/tools/perf/util/intel-pt-decoder/insn.c
>index 47314a6..9f26eae 100644
>--- a/tools/perf/util/intel-pt-decoder/insn.c
>+++ b/tools/perf/util/intel-pt-decoder/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:
It ought to be made specific as __s8 (or int8_t) really...
--
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