Re: [PATCH v2] powerpc/boot: Delete unneeded .globl _zimage_start

On Thu, Mar 26, 2020 at 03:26:12PM -0700, Fangrui Song wrote:

On 2020-03-26, Segher Boessenkool wrote:

quoted

On Wed, Mar 25, 2020 at 09:42:57AM -0700, Fangrui Song wrote:

quoted

.globl sets the symbol binding to STB_GLOBAL while .weak sets the
binding to STB_WEAK. GNU as let .weak override .globl since binutils-gdb
5ca547dc2399a0a5d9f20626d4bf5547c3ccfddd (1996). Clang integrated
assembler let the last win but it may error in the future.

GNU AS works for more than just ELF.  The way the assembler language
is defined, it is not .weak overriding .globl -- instead, .weak sets a
symbol attribute.  On an existing symbol (but it creates on if there is
none yet).

Clang is buggy if it does not allow valid (and perfectly normal)
assembler code like this.

https://sourceware.org/pipermail/binutils/2020-March/110399.html

Alan: "I think it is completely fine for you to make the llvm assembler
error on inconsistent binding, or the last directive win.  Either of
those behaviours is logical and good, but you quite possibly will run
into a need to fix more user assembly.

This would be fine and consistent behaviour, of course.  But it is not
appropriate if you want to pretend to be compatible to GNU toolchains.

Which is exactly why you want this kernel patch at all.  And the kernel
can (in this case) accommodate your buggy assembler, sure, but are you
going to "fix" all other programs with this "problem" as well?


Segher