From: Peter Zijlstra <peterz@infradead.org>
To: Fangrui Song <maskray@google.com>
Cc: x86@kernel.org, Josh Poimboeuf <jpoimboe@kernel.org>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH] x86/speculation, objtool: Use absolute relocations for annotations
Date: Thu, 21 Sep 2023 21:22:53 +0200 [thread overview]
Message-ID: <20230921192253.GA39480@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <CAFP8O3JpkWTXnxYxa45uANNMQ34g2VUPnfj7-oWn3oq9egUb-A@mail.gmail.com>
On Thu, Sep 21, 2023 at 10:36:27AM -0700, Fangrui Song wrote:
> Well, only if the clever assembler doesn't support 32-bit absolute
> relocation for a 64-bit architecture.
> I don't know such an architecture. In addition, as long as the
> architecture intends to support DWARF32, it has to support 32-bit
> absolute relocations for a 64-bit architecture.
Ooh... my bad. For some reason I thought that absolute meant native word
size. But you already mentioned R_X86_64_32 (and I failed to check) and
that is indeed an absolute (S+A) relocation of 32bit (dword) size.
And apparently we also have R_X64_64_16 and R_X86_64_8, which would even
allow something like:
#define OBJTOOL_ANNOTATE(type) \
"999:\n\t" \
".pushsection .discard.objtool_annotate\n\t" \
".byte 999b\n\t" \
".byte " __stringify(type) "\n\t" \
".popsection\n\t"
And since we only read the relocation and don't care for the actual
result that would actually work just fine.
Anyway, thanks for bearing with me.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
next prev parent reply other threads:[~2023-09-21 19:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-20 0:17 [PATCH] x86/speculation, objtool: Use absolute relocations for annotations Fangrui Song
2023-09-21 7:12 ` [tip: objtool/core] " tip-bot2 for Fangrui Song
2023-09-21 7:27 ` Peter Zijlstra
2023-09-21 8:03 ` Ingo Molnar
2023-09-21 7:26 ` [PATCH] " Peter Zijlstra
2023-09-21 7:58 ` Fangrui Song
2023-09-21 15:35 ` Peter Zijlstra
2023-09-21 16:26 ` Fangrui Song
2023-09-21 17:19 ` Peter Zijlstra
2023-09-21 17:36 ` Fangrui Song
2023-09-21 19:22 ` Peter Zijlstra [this message]
2023-09-21 19:31 ` Peter Zijlstra
2023-09-21 20:07 ` Fangrui Song
2023-09-21 20:18 ` Peter Zijlstra
2023-09-22 9:51 ` [tip: objtool/core] " tip-bot2 for Fangrui Song
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