Rework alignment handling in __libc_allocate_tls() for Variant I of TLS layout.
There are two versions of variant I of TLS
- ARM and aarch64 uses original version of variant I here TP points to start of TCB followed by aligned TLS segment. Both TCB and TLS must be aligned to alignment of TLS section. The TCB points to DTV vector and DTV values are real addresses (without bias).
- MIPS, PowerPC and RISC-V uses modified, incomatible version of variant I, where TP points (with bias) to TLS and TCB immediately precedes TLS without any alignment gap. Only TLS should be aligned. The TCB points to DTV vector and DTV values are biased by constant value (0x8000) from real addresses.
Take this in account when allocating memory for TLS structures.
MFC after: 1 month
There are at least one oustanding issue: I cannot find any evidence
if a DTV vector is used in Local Exec TLS Model and if so, whether
is expected that it contains biased TLS values (addresses).