(original) (raw)

My own preference is for a warning, that way the issue is visible and the programmer can choose to ignore it, disable it or make it an error as preferred.

I tried it with embedded NUL characters, and this turned out not to be a good idea. The example:

\_\_attribute\_\_((section("grok\\nfubar\\0poisoned\\tsnafu")))

int foo() { return 42; }

with clang v3.8.0 for X86 ‘clang -Wall -S section.c’ I get the following output and no warnings:

.text

.def foo;

.scl 2;

.type 32;

.endef

.section grok

fubar,"xr"

.globl foo

.align 16, 0x90

foo: # @foo

.Ltmp0:

.seh\_proc foo

# BB#0: # %entry

.Ltmp1:

.seh\_endprologue

movl $42, %eax

retq

.seh\_handlerdata

.section grok

fubar,"xr"

.Ltmp2:

.seh\_endproc

Since we do not have an integrated assembler, we have to go through the emit-assembly and separate invocation of the assembler, and such constructs fail at the next level.

I don’t know, perhaps when the compiler is writing object code directly it can somehow make the whole string meaningful as a section name, though I’m not sure how I could write an LD script for such sections.

I don’t advocate the programmer doing this kind of trick to force assembly code into the emitted assembly code; it seems very dangerous. The ‘\_\_attribute\_\_((naked))’ was changed a few versions ago so that a function defined with this attribute could not contain C source code. I haven’t experimented with it since then.

Thanks,

MartinO

From: llvm-dev \[mailto:llvm-dev-bounces@lists.llvm.org\] On Behalf Of mats petersson via llvm-dev
Sent: 05 October 2016 21:48
To: Joerg Sonnenberger ; llvm-dev
Subject: Re: \[llvm-dev\] Using '\_\_attribute\_\_((section("name")))' for inline assembly injection