Exception::CallStack: avoid allocations in LibC.dl_iterate_phdr

[dmgk]

Calling self.read_dwarf_sections directly from the C callback may lead to reallocations and deadlocks due to the internal lock held by dl_iterate_phdr (#10084). Work around this by storing object base address and passing it to self.read_dwarf_sections later when dl_iterate_phdr returns.

This also fixes #12329 because there's no need to disable GC around dl_iterate_phdr anymore.

[HertzDevil]

I would avoid using a TypeDeclaration here unless necessary:

Suggested change

	base_address : LibC::Elf_Addr = 0
	base_address = LibC::Elf_Addr.zero

[straight-shoota]

Later we're passing a pointer to this variable. So IMO it makes sense to pin its type in order to prevent an accidental union type tainting the pointer.

[beta-ziliani]

Is it OK to only call read_dwarf_sections with the last address provided by dl_iterate_phdr? IIUC, that's what this change is introducing. Before it was calling read_dwarf_sections for each object loaded.

[dmgk]

@beta-ziliani No, the original code was also stopping after reading the first object. Quoting dl_iterate_phdr(3):

The dl_iterate_phdr() function walks through the list of an
application's shared objects and calls the function callback once
for each object, until either all shared objects have been
processed or callback returns a nonzero value.

[beta-ziliani]

Totally missed that, thanks!