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From: Peter Zijlstra <peterz@infradead.org>
To: jpoimboe@redhat.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mbenes@suse.cz
Subject: [PATCH 2/2] objtool: Optimize/fix retpoline alternative generation
Date: Thu, 07 Oct 2021 23:22:13 +0200	[thread overview]
Message-ID: <20211007212627.008917519@infradead.org> (raw)
In-Reply-To: <20211007212211.366874577@infradead.org>

When re-running objtool it will generate alterantives for all
retpoline hunks, even if they are already present.

Discard the retpoline alternatives later so we can mark the
instructions as already having alternatives and subsequently skip
generating them. Use ->ignore_alts for this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 tools/objtool/arch/x86/decode.c |    3 +++
 tools/objtool/check.c           |    8 ++++++++
 tools/objtool/special.c         |    8 --------
 3 files changed, 11 insertions(+), 8 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -806,6 +806,9 @@ int arch_rewrite_retpolines(struct objto
 		if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk"))
 			continue;
 
+		if (insn->ignore_alts)
+			continue;
+
 		reloc = insn->reloc;
 
 		sprintf(name, "__x86_indirect_alt_%s_%s",
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1468,6 +1468,14 @@ static int add_special_section_alts(stru
 				ret = -1;
 				goto out;
 			}
+			/*
+			 * Skip (but mark) the retpoline alternatives so that we
+			 * don't generate them again.
+			 */
+			if (new_insn->func && arch_is_retpoline(new_insn->func)) {
+				orig_insn->ignore_alts = true;
+				continue;
+			}
 		}
 
 		if (special_alt->group) {
--- 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 */



  parent reply	other threads:[~2021-10-07 21:27 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-07 21:22 [PATCH 0/2] objtool: Avoid pointless modifications Peter Zijlstra
2021-10-07 21:22 ` [PATCH 1/2] objtool: Optimize re-writing jump_label Peter Zijlstra
2021-10-08  6:55   ` Josh Poimboeuf
2021-10-08 10:03     ` Peter Zijlstra
2021-10-08 16:28       ` Josh Poimboeuf
2021-10-07 21:22 ` Peter Zijlstra [this message]
2021-10-08  7:23   ` [PATCH 2/2] objtool: Optimize/fix retpoline alternative generation Josh Poimboeuf
2021-10-08 10:35     ` Peter Zijlstra
2021-10-08 16:39       ` Josh Poimboeuf
2021-10-09 10:42         ` Peter Zijlstra

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