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Date: Mon, 21 Apr 2014 16:25:32 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: _start(ldso) & _start(crt)
On Mon, Apr 21, 2014 at 03:41:23PM -0400, writeonce@...ipix.org wrote:
> Greetings,
>
> When running a dynamically linked program, the general control flow is
>
> _start(ldso/{arch}/start.s) --> __dynlink --> _start(crt) -->
> __libc_start_main --> main()
>
> When asking gdb to set up a breakpoint at _start (b _start), gdb's
> confirmation message shows the address of _start(crt), but it then
> breaks at _start(ldso), which is actually what I want. It then
> later also breaks at _start(crt).
>
> If gdb decided to only break at the executable's _start, then I
> believe there would be no way to request a break at the
> interpreter's (ldso) _start routine, since the address of ldso's
> _start is not known prior to execution.
>
> I am not sure whether this is a good-enough motivation to rename
> ldso's start to _ldso_start (and set libc.so's entry point
> accordingly), or whether we could simply count on gdb and other
> debuggers to continue to do the "right thing" by breaking at the
> earlier _start of the two. For one thing, setting a breakpoint at
> __dynlink provides pretty much the same debugging ability as with
> _start(ldso), and does not require any changes. Any thoughts?
The motivation for the name _start in the dynamic linker was
presumably that it gets used by default as the entry point, but we
already have -Wl,-e,_start anyway, so I don't see any compelling
reason it couldn't be renamed. Does anyone else object to changing it?
Rich
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