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Date: Thu, 14 Oct 2021 17:43:25 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: x86@...nel.org, andrew.cooper3@...rix.com,
linux-kernel@...r.kernel.org, alexei.starovoitov@...il.com,
ndesaulniers@...gle.com
Subject: Re: [PATCH 1/9] objtool,x86: Replace alternatives with
.retpoline_sites
On Wed, Oct 13, 2021 at 01:11:35PM -0700, Josh Poimboeuf wrote:
> Guess it shouldn't be called arch_rewrite_retpolines() anymore. And it
> can be moved to check.c next to create_static_call_sections().
>
> Also is it possible to remove the arch_is_retpoline() check in
> get_alt_entry()? I'm having trouble remembering why that was needed in
> the first place.
Makes sense...
---
+++ b/tools/objtool/arch/x86/decode.c
@@ -711,52 +711,6 @@ const char *arch_ret_insn(int len)
return ret[len-1];
}
-int arch_rewrite_retpolines(struct objtool_file *file)
-{
- struct instruction *insn;
- struct section *sec;
- int idx;
-
- sec = find_section_by_name(file->elf, ".retpoline_sites");
- if (sec) {
- WARN("file already has .retpoline_sites, skipping");
- return 0;
- }
-
- idx = 0;
- list_for_each_entry(insn, &file->retpoline_call_list, call_node)
- idx++;
-
- if (!idx)
- return 0;
-
- sec = elf_create_section(file->elf, ".retpoline_sites", 0,
- sizeof(int), idx);
- if (!sec) {
- WARN("elf_create_section: .retpoline_sites");
- return -1;
- }
-
- idx = 0;
- list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
-
- int *site = (int *)sec->data->d_buf + idx;
- *site = 0;
-
- if (elf_add_reloc_to_insn(file->elf, sec,
- idx * sizeof(int),
- R_X86_64_PC32,
- insn->sec, insn->offset)) {
- WARN("elf_add_reloc_to_insn: .retpoline_sites");
- return -1;
- }
-
- idx++;
- }
-
- return 0;
-}
-
int arch_decode_hint_reg(u8 sp_reg, int *base)
{
switch (sp_reg) {
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -683,6 +683,52 @@ static int create_static_call_sections(s
return 0;
}
+static int create_retpoline_sites_sections(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct section *sec;
+ int idx;
+
+ sec = find_section_by_name(file->elf, ".retpoline_sites");
+ if (sec) {
+ WARN("file already has .retpoline_sites, skipping");
+ return 0;
+ }
+
+ idx = 0;
+ list_for_each_entry(insn, &file->retpoline_call_list, call_node)
+ idx++;
+
+ if (!idx)
+ return 0;
+
+ sec = elf_create_section(file->elf, ".retpoline_sites", 0,
+ sizeof(int), idx);
+ if (!sec) {
+ WARN("elf_create_section: .retpoline_sites");
+ return -1;
+ }
+
+ idx = 0;
+ list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
+
+ int *site = (int *)sec->data->d_buf + idx;
+ *site = 0;
+
+ if (elf_add_reloc_to_insn(file->elf, sec,
+ idx * sizeof(int),
+ R_X86_64_PC32,
+ insn->sec, insn->offset)) {
+ WARN("elf_add_reloc_to_insn: .retpoline_sites");
+ return -1;
+ }
+
+ idx++;
+ }
+
+ return 0;
+}
+
static int create_mcount_loc_sections(struct objtool_file *file)
{
struct section *sec;
@@ -1950,11 +1996,6 @@ static void mark_rodata(struct objtool_f
file->rodata = found;
}
-__weak int arch_rewrite_retpolines(struct objtool_file *file)
-{
- return 0;
-}
-
static int decode_sections(struct objtool_file *file)
{
int ret;
@@ -2027,15 +2068,6 @@ static int decode_sections(struct objtoo
if (ret)
return ret;
- /*
- * Must be after add_special_section_alts(), since this will emit
- * alternatives. Must be after add_{jump,call}_destination(), since
- * those create the call insn lists.
- */
- ret = arch_rewrite_retpolines(file);
- if (ret)
- return ret;
-
return 0;
}
@@ -3438,6 +3470,13 @@ int check(struct objtool_file *file)
goto out;
warnings += ret;
+ if (retpoline) {
+ ret = create_retpoline_sites_sections(file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+ }
+
if (mcount) {
ret = create_mcount_loc_sections(file);
if (ret < 0)
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -109,14 +109,6 @@ static int get_alt_entry(struct elf *elf
return -1;
}
- /*
- * Skip retpoline .altinstr_replacement... we already rewrite the
- * instructions for retpolines anyway, see arch_is_retpoline()
- * usage in add_{call,jump}_destinations().
- */
- if (arch_is_retpoline(new_reloc->sym))
- return 1;
-
reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off);
/* _ASM_EXTABLE_EX hack */
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