From: Segher Boessenkool <segher@kernel•crashing.org>
To: Peter Zijlstra <peterz@infradead•org>
Cc: Sathvika Vasireddy <sv@linux•ibm.com>,
nathan@kernel•org, nsc@kernel•org, maddy@linux•ibm.com,
mpe@ellerman•id.au, npiggin@gmail•com, chleroy@kernel•org,
jpoimboe@kernel•org, ojeda@kernel•org, masahiroy@kernel•org,
lossin@kernel•org, tamird@kernel•org,
thomas.weissschuh@linutronix•de, rostedt@goodmis•org,
ihor.solodrai@linux•dev, thuth@redhat•com, pmladek@suse•com,
aliceryhl@google•com, elver@google•com, kees@kernel•org,
legion@kernel•org, ardb@kernel•org, yuxuan.zuo@outlook•com,
alexghiti@rivosinc•com, alexandre.chartre@oracle•com,
bp@alien8•de, linux-kbuild@vger•kernel.org,
linux-kernel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH v1 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets
Date: Tue, 5 May 2026 10:56:58 -0500 [thread overview]
Message-ID: <afoTSvawD4CXCCy1@gate> (raw)
In-Reply-To: <20260505144539.GX3126523@noisy.programming.kicks-ass.net>
Hi!
On Tue, May 05, 2026 at 04:45:39PM +0200, Peter Zijlstra wrote:
> On Tue, May 05, 2026 at 02:16:23PM +0530, Sathvika Vasireddy wrote:
> > switch (opcode) {
> > + case 16:
>
> Like case 18 below, this wants a comment describing which instruction
> this is; bclr ?
Yes. It is 19/16, b[c]lr (primary opcode 19, secondary opcode 16).
Where is it described what INSN_RETURN actually means for objtool? Not
in the header file :-(
For PowerPC, all three of b[c]lr[l], b[c]ctr[l], and b[c]tar[l] are
indirect jumps, to an address in a register. They do absolutely nothing
typically done in a function epilog, like "return" insns in some other
archs do. But the BH field ("branch hint") in the instruction helps
predict the control flow involving the insn as something in a call and
return pattern :-)
Segher
next prev parent reply other threads:[~2026-05-05 15:58 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-05 8:46 [PATCH v1 0/6] objtool: Fixup alternate feature relative addresses Sathvika Vasireddy
2026-05-05 8:46 ` [PATCH v1 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets Sathvika Vasireddy
2026-05-05 14:45 ` Peter Zijlstra
2026-05-05 14:49 ` Peter Zijlstra
2026-05-05 15:48 ` Christophe Leroy (CS GROUP)
2026-05-06 7:17 ` Peter Zijlstra
2026-05-06 14:28 ` Segher Boessenkool
2026-05-05 15:56 ` Segher Boessenkool [this message]
2026-05-06 7:00 ` Peter Zijlstra
2026-05-06 13:58 ` Segher Boessenkool
2026-05-06 14:22 ` Peter Zijlstra
2026-05-06 14:42 ` Segher Boessenkool
2026-05-05 8:46 ` [PATCH v1 2/6] objtool: Set ELF_F_LAYOUT flag to preserve vmlinux segment layout Sathvika Vasireddy
2026-05-05 8:46 ` [PATCH v1 3/6] objtool: Fix "can't find starting instruction" warnings on vmlinux Sathvika Vasireddy
2026-05-05 8:46 ` [PATCH v1 4/6] objtool/powerpc: Skip jump destination analysis and unnanotated intra-function call warnings for --ftr-fixup Sathvika Vasireddy
2026-05-05 8:46 ` [PATCH v1 5/6] kbuild: Add objtool integration for PowerPC feature fixups Sathvika Vasireddy
2026-05-05 8:46 ` [PATCH v1 6/6] powerpc: Enable build-time feature fixup processing by default Sathvika Vasireddy
2026-05-05 9:05 ` [PATCH v1 0/6] objtool: Fixup alternate feature relative addresses Christophe Leroy (CS GROUP)
2026-05-05 11:40 ` Peter Zijlstra
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