[libc] fix tls teardown while being used (#108229)

The call chain to `Mutex:lock` can be polluted by stack protector. For
completely safe, let's postpone the main TLS tearing down to a separate
ph

[libc] fix tls teardown while being used (#108229)

The call chain to `Mutex:lock` can be polluted by stack protector. For
completely safe, let's postpone the main TLS tearing down to a separate
phase.

fix #108030

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Revert "libc: Remove `extern "C"` from main declarations" (#102827)

Reverts llvm/llvm-project#102825

libc: Remove `extern "C"` from main declarations (#102825)

This is invalid in C++, and clang recently started warning on it as of
#101853

[libc][startup] fix main thread TLS unmapped with wrong value (#102009)

We have been unmapping a wrong address all the time.
```c
munmap(0x704cffebb000, 41048) = 0
munmap(0x704cffec6000

[libc][startup] fix main thread TLS unmapped with wrong value (#102009)

We have been unmapping a wrong address all the time.
```c
munmap(0x704cffebb000, 41048) = 0
munmap(0x704cffec6000, 69632) = 0
munmap(0x704cffe9f000, 41048) = 0
munmap(0x704cffeaa000, 69632) = 0
munmap(0x704cffe83000, 41048) = 0
munmap(0x704cffe8e000, 69632) = 0
munmap(0x704cffe67000, 41048) = 0
munmap(0x704cffe72000, 69632) = 0
munmap(0x704cffe4b000, 41048) = 0
munmap(0x704cffe56000, 69632) = 0
munmap(0x704cffe2f000, 41048) = 0
munmap(0x704cffe3a000, 69632) = 0
munmap(0x704cfff51028, 41048) = -1 EINVAL (Invalid argument)
```

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revert all tid changes (#100915)

reland "[libc] implement cached process/thread identity (#98989)" (#99765)

Revert "[libc] implement cached process/thread identity" (#99559)

Reverts llvm/llvm-project#98989

[libc] implement cached process/thread identity (#98989)

migrated from https://github.com/llvm/llvm-project/pull/95965 due to
corrupted git history

[libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration (#98597)

This is a part of #97655.

Revert "[libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration" (#98593)

Reverts llvm/llvm-project#98075

bots are broken

[libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration (#98075)

This is a part of #97655.

[libc][arm32] define argc type and stack alignment (#96367)

https://github.com/ARM-software/abi-aa/blob/main/aapcs32/aapcs32.rst#6212stack-constraints-at-a-public-interface
mentions that the stack o

[libc][arm32] define argc type and stack alignment (#96367)

https://github.com/ARM-software/abi-aa/blob/main/aapcs32/aapcs32.rst#6212stack-constraints-at-a-public-interface
mentions that the stack on ARM32 is double word aligned.

Remove confused comments around ArgcType. argc is always an int, passed on the
stack, so we need to store a pointer to it (regardless of ILP32 or LP64).

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[libc][startup] create header for ElfW and use in startup (#96510)


This is necessary for 32b platforms such as ARM and i386.

Link: #94128

[libc][NFC] remove TODO about AppProperties (#79356)

```
AppProperties app;
```
is marked as a weak symbol in header now. One can just use `&app !=
nullptr` to check if `app` is defined. There i

[libc][NFC] remove TODO about AppProperties (#79356)

```
AppProperties app;
```
is marked as a weak symbol in header now. One can just use `&app !=
nullptr` to check if `app` is defined. There is no need to define it for
overlay mode.

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[libc] support PIE relocations (#78993)

For some reasons, we are using `-fpie`
(libc/cmake/modules/LLVMLibCObjectRules.cmake:31) without supporting it.
According to @lntue, some of the hermetic test

[libc] support PIE relocations (#78993)

For some reasons, we are using `-fpie`
(libc/cmake/modules/LLVMLibCObjectRules.cmake:31) without supporting it.
According to @lntue, some of the hermetic tests are broken without
proper PIE support. This patch implements basic relocations support for
PIE.

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[libc] major refactor of startup library (#76092)

* separate initialization routines into _start and do_start for all
architectures.
* lift do_start as a separate object library to avoid code dupl

[libc] major refactor of startup library (#76092)

* separate initialization routines into _start and do_start for all
architectures.
* lift do_start as a separate object library to avoid code duplication.
* (addtionally) address the problem of building hermetic libc with
-fstack-pointer-*

The `crt1.o` is now a merged result of three components:

```
___
|___ x86_64
| |_______ start.cpp.o <- _start (loads process initial stack and aligns stack pointer)
| |_______ tls.cpp.o <- init_tls, cleanup_tls, set_thread_pointer (TLS related routines)
|___ do_start.cpp.o <- do_start (sets up global variables and invokes the main function)
```

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