[elf2] implement __start_SECNAME and __stop_SECNAME

[silvasean]

Bugzilla Link	25188
Resolution	FIXED
Resolved on	Oct 16, 2015 20:52
Version	unspecified
OS	All
Blocks	#23588
CC	@Bigcheese,@hfinkel,@rui314

Extended Description

This is required by D13329 (r250200).

In D13329, the following quote from Ian Taylor:

"When a section name is a valid C identifier, the linker automatically provides __start and __stop symbols set to the addresses of the beginning and end of the section. The symbols are __start_SECNAME and __stop_SECNAME where SECNAME is the name of the section.

This is not defined by the ELF ABI, but it is completely reliable on
GNU/Linux. In fact it is reliable on any ELF system except possibly
Solaris, and it probably works on Solaris too. This is definitely
what you should do instead of using a linker script. It's more
reliable and more efficient, and it's what everybody else does"

[rui314]

It should be easy to implement that, but do you know any program that actually uses his feature?

[rui314]

Ah, sorry, http://reviews.llvm.org/D13329 is the example as you wrote. I'll try to implement this.

[silvasean]

Do you know if Ian is referring to "input sections" or "output sections" when he says "sections"?

[rui314]

It seems that "section name" means "output section name". I can link this code with gold, but if I rename input section "foo" to "bar" using linker script, it failed to link because __{start,stop}_foo no longer exist.

.global _start
.text
_start:
call __start_foo
call __stop_foo

.section foo,"ax"
nop

[rui314]

http://reviews.llvm.org/D13760

[rui314]

Implemented in r250432.