The kernel sets r7 to 0 (success) or -1 (error), and stores the result in r2.
When r7 is -1 and the result is positive, it needs to be negated to get the
errno value that higher-level code, such as errnoFromSyscall(), expects to see.
The old code was missing the check that r2 is positive, but was also doing the
r7 check incorrectly; since it can only be set to 0 or -1, the blez instruction
would always branch.
In practice, this fix is necessary for e.g. the ENOSYS error to be interpreted
correctly. This manifested as hitting an unreachable branch when calling
process_vm_readv() in std.debug.MemoryAccessor.
The signature is documented as:
int link(const char *, const char *);
(see https://man7.org/linux/man-pages/man2/link.2.html or https://man.netbsd.org/link.2)
And its not some Linux extension, the [syscall
implementation](21b136cc63/fs/namei.c (L4794-L4797))
only expects two arguments too.
It probably *should* have a flags parameter, but its too late now.
I am a bit surprised that linking glibc or musl against code that invokes
a 'link' with three parameters doesn't fail (at least, I couldn't get any
local test cases to trigger a compile or link error).
The test case in std/posix/test.zig is currently disabled, but if I
manually enable it, it works with this change.
`__xl_a` is just a global variable containing a null function pointer. There's
nothing magical about it or its name at all.
The section names used on `__xl_a` and `__xl_b` (`.CRT$XLA` and `.CRT$XLZ`) are
the real magic here. The compiler emits TLS variables into `.CRT$XL<x>`
sections, where `x` is an uppercase letter between A and Z (exclusive). The
linker then sorts those sections alphabetically (due to the `$`), and the result
is a neat array of TLS initialization callbacks between `__xl_a` and `__xl_z`.
That array is null-terminated, though! Normally, `__xl_z` serves as the null
terminator; however, by pointing `AddressesOfCallBacks` to `__xl_a`, which just
contains a null function pointer, we've effectively made it so that the PE
loader will just immediately stop invoking TLS callbacks. Fix that by pointing
to the first actual TLS callback instead (or `__xl_z` if there are none).
If there is a VDSO, it will have clock_gettime(). The main thing we're concerned
about is architectures that don't have a VDSO at all, of which there are a few.
* Rename isPPC() -> isPowerPC32().
* Rename isPPC64() -> isPowerPC64().
* Add new isPowerPC() function which covers both.
There was confusion even in the standard library about what isPPC() meant. This
change makes these functions work how I think most people actually expect them
to work, and makes them consistent with isMIPS(), isSPARC(), etc.
I chose to rename from PPC to PowerPC because 1) it's more consistent with the
other functions, and 2) it'll cause loud rather than silent breakage for anyone
who might have been depending on isPPC() while misunderstanding it.
