linux-kernel - Re: [RFC PATCH] objtool: Skip unannotated intra-function call warning for bl+mflr pattern

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Message-ID: <20250224123534.GB17456@noisy.programming.kicks-ass.net>
Date: Mon, 24 Feb 2025 13:35:34 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Sathvika Vasireddy <sv@...ux.ibm.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, christophe.leroy@...roup.eu,
	npiggin@...il.com, maddy@...ux.ibm.com,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	llvm@...ts.linux.dev
Subject: Re: [RFC PATCH] objtool: Skip unannotated intra-function call
 warning for bl+mflr pattern

On Fri, Feb 21, 2025 at 02:20:41PM +0530, Sathvika Vasireddy wrote:

> Also, just out of curiosity, how does x86 do it? Does it not use a branch to
> next instruction approach?

x86_64 can use LEA like:

  #define _THIS_IP_ ({ unsigned long __here; asm ("lea 0(%%rip), %0" : "=r" (__here)); __here; })

32bit needs to call a function, read the stack value and return.