From: Arvind Sankar <nivedita@alum.mit.edu>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, tglx@linutronix.de, linux-kernel@vger.kernel.org,
mingo@kernel.org, hpa@zytor.com, ast@kernel.org,
peterz@infradead.org, rdunlap@infradead.org,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: BPF vs objtool again
Date: Wed, 29 Apr 2020 18:01:51 -0400 [thread overview]
Message-ID: <20200429220151.GA1642005@rani.riverdale.lan> (raw)
In-Reply-To: <20200429215159.eah6ksnxq6g5adpx@treble>
On Wed, Apr 29, 2020 at 04:51:59PM -0500, Josh Poimboeuf wrote:
> On Thu, Jul 18, 2019 at 12:14:08PM -0700, tip-bot for Josh Poimboeuf wrote:
> > Commit-ID: 3193c0836f203a91bef96d88c64cccf0be090d9c
> > Gitweb: https://git.kernel.org/tip/3193c0836f203a91bef96d88c64cccf0be090d9c
> > Author: Josh Poimboeuf <jpoimboe@redhat.com>
> > AuthorDate: Wed, 17 Jul 2019 20:36:45 -0500
> > Committer: Thomas Gleixner <tglx@linutronix.de>
> > CommitDate: Thu, 18 Jul 2019 21:01:06 +0200
> >
> > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()
>
> For some reason, this
>
> __attribute__((optimize("-fno-gcse")))
>
> is disabling frame pointers in ___bpf_prog_run(). If you compile with
> CONFIG_FRAME_POINTER it'll show something like:
>
> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run.cold()+0x7: call without frame pointer save/setup
>
> Also, since GCC 9.1, the GCC docs say "The optimize attribute should be
> used for debugging purposes only. It is not suitable in production
> code." That doesn't sound too promising.
>
It turns out that the optimize attribute doesn't append options to the
command-line arguments, it starts from the defaults and only adds
whatever you specify in the attribute. So it's not very useful for
production code.
See this for eg where the same thing came up in a different context.
https://lore.kernel.org/lkml/alpine.LSU.2.21.2004151445520.11688@wotan.suse.de/
next prev parent reply other threads:[~2020-04-29 22:01 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 1:36 [PATCH v2 00/22] x86, objtool: several fixes/improvements Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 01/22] x86/paravirt: Fix callee-saved function ELF sizes Josh Poimboeuf
2019-07-18 19:07 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 02/22] x86/kvm: Fix fastop function ELF metadata Josh Poimboeuf
2019-07-18 19:08 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 03/22] x86/kvm: Replace vmx_vmenter()'s call to kvm_spurious_fault() with UD2 Josh Poimboeuf
2019-07-18 8:17 ` Paolo Bonzini
2019-07-18 19:08 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 04/22] x86/kvm: Don't call kvm_spurious_fault() from .fixup Josh Poimboeuf
2019-07-18 8:22 ` Paolo Bonzini
2019-07-18 13:16 ` Sean Christopherson
2019-07-18 13:18 ` Paolo Bonzini
2019-07-18 14:12 ` Josh Poimboeuf
2019-07-18 14:13 ` Paolo Bonzini
2019-07-18 14:03 ` Josh Poimboeuf
2019-07-18 19:09 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 05/22] x86/entry: Fix thunk function ELF sizes Josh Poimboeuf
2019-07-18 19:10 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 06/22] x86/head/64: Annotate start_cpu0() as non-callable Josh Poimboeuf
2019-07-18 19:11 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 07/22] x86/uaccess: Remove ELF function annotation from copy_user_handle_tail() Josh Poimboeuf
2019-07-18 19:11 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 08/22] x86/uaccess: Don't leak AC flag into fentry from mcsafe_handle_tail() Josh Poimboeuf
2019-07-18 19:12 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 09/22] x86/uaccess: Remove redundant CLACs in getuser/putuser error paths Josh Poimboeuf
2019-07-18 19:13 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 10/22] bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() Josh Poimboeuf
2019-07-18 19:14 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2020-04-29 21:51 ` BPF vs objtool again Josh Poimboeuf
2020-04-29 22:01 ` Arvind Sankar [this message]
2020-04-29 23:41 ` Alexei Starovoitov
2020-04-30 0:13 ` Josh Poimboeuf
2020-04-30 2:10 ` Alexei Starovoitov
2020-04-30 3:53 ` Josh Poimboeuf
2020-04-30 4:24 ` Alexei Starovoitov
2020-04-30 4:43 ` Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 11/22] objtool: Add mcsafe_handle_tail() to the uaccess safe list Josh Poimboeuf
2019-07-18 19:14 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 12/22] objtool: Track original function across branches Josh Poimboeuf
2019-07-18 19:15 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 13/22] objtool: Refactor function alias logic Josh Poimboeuf
2019-07-18 19:16 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 14/22] objtool: Warn on zero-length functions Josh Poimboeuf
2019-07-18 19:17 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 15/22] objtool: Change dead_end_function() to return boolean Josh Poimboeuf
2019-07-18 19:17 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 16/22] objtool: Do frame pointer check before dead end check Josh Poimboeuf
2019-07-18 19:18 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 17/22] objtool: Refactor sibling call detection logic Josh Poimboeuf
2019-07-18 19:19 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 18/22] objtool: Refactor jump table code Josh Poimboeuf
2019-07-18 19:20 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 19/22] objtool: Support repeated uses of the same C jump table Josh Poimboeuf
2019-07-18 19:20 ` [tip:core/urgent] " tip-bot for Jann Horn
2019-07-18 1:36 ` [PATCH v2 20/22] objtool: Fix seg fault on bad switch table entry Josh Poimboeuf
2019-07-18 19:21 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 21/22] objtool: convert insn type to enum Josh Poimboeuf
2019-07-18 19:22 ` [tip:core/urgent] objtool: Convert " tip-bot for Josh Poimboeuf
2019-07-18 1:36 ` [PATCH v2 22/22] objtool: Support conditional retpolines Josh Poimboeuf
2019-07-18 19:23 ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
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