Each TLSDESC relocation relocates a 2-word descriptor in the GOT that
contains:
- the address of a TLS resolver function
- an argument to pass (indirectly) to the resolver function
(Specifically, the address of the 2-word descriptor is passed to the
resolver.)
The loader resolves R_GENERIC_TLSDESC relocations using one of three
resolver functions that it defines:
- tlsdesc_resolver_static
- tlsdesc_resolver_dynamic
- tlsdesc_resolver_unresolved_weak
The resolver functions are written in assembly because they have a
restrictive calling convention. They're only allowed to modify x0 and
(apparently) the condition codes.
For a relocation to memory in static TLS (i.e. the executable or an solib
loaded initially), the loader uses a simple resolver function,
tlsdesc_resolver_static, that returns the static offset it receives from
the loader.
For relocations to dynamic TLS memory (i.e. memory in a dlopen'ed solib),
the loader uses tlsdesc_resolver_dynamic, which allocates TLS memory on
demand. It inlines the fast path of __tls_get_addr, then falls back to
__tls_get_addr when it needs to allocate memory. The loader handles these
dynamic TLS relocations in two passes:
- In the first pass, it allocates a table of TlsDynamicResolverArg
objects, one per dynamic TLSDESC relocation.
- In the second pass, once the table is finalized, it writes the
addresses of the TlsDynamicResolverArg objects into the TLSDESC
relocations.
tlsdesc_resolver_unresolved_weak returns a negated thread pointer so that
taking the address of an unresolved weak TLS symbols produces NULL.
The loader handles R_GENERIC_TLSDESC in a target-independent way, but
only for arm64, because Bionic has only implemented the resolver functions
for arm64.
Bug: http://b/78026329
Test: bionic unit tests
Test: check that backtrace works inside a resolver function and inside
__tls_get_addr called from a resolver
(gdbclient.py, b __tls_get_addr, bt)
Merged-In: I752e59ff986292449892c449dad2546e6f0ff7b6
Change-Id: I752e59ff986292449892c449dad2546e6f0ff7b6
I noticed that sometimes the old unwinder will add an extra PC 0 frame
after this change, but the new unwinder works in all cases. I'm not going
to fix the old unwinder since I plan to remove it very soon.
Bug: 67784501
Test: Forced a crash in the linker and verified that the unwind
Test: stops in __dl_start. Tested on arm/aarch64/x86/x86_64.
Change-Id: Id6585768023256be5c1d341df7b06b786a220b40
There's no need: __linker_init only takes one argument.
Also remove the arm __CTOR_LIST__; we use .init_array and .fini_array instead
of .ctor and .dtor anyway, and I don't think we've ever supported the latter.
Change-Id: Ifc91a5a90c6aa39d674bf0509a7af2e1ff0beddd
Our <machine/asm.h> files were modified from upstream, to the extent
that no architecture was actually using the upstream ENTRY or END macros,
assuming that architecture even had such a macro upstream. This patch moves
everyone to the same macros, with just a few tweaks remaining in the
<machine/asm.h> files, which no one should now use directly.
I've removed most of the unused cruft from the <machine/asm.h> files, though
there's still rather a lot in the mips/mips64 ones.
Bug: 12229603
Change-Id: I2fff287dc571ac1087abe9070362fb9420d85d6d
