This prevents it from trying to access thread local storage before it
has set up thread local storage, particularly when code coverage
instrumentation is enabled.
The previous version of this function referenced the argc_argv_ptr global
variable as an inline asm operand. This caused LLVM to generate prologue code to
initialize the ToC so that the global variable can actually be accessed.
Ordinarily, there's nothing wrong with that. But _start() is a naked function!
This makes it actually super surprising that LLVM did this. It also means that
the old version only really worked by accident.
Once the reference to the global variable was removed, no ToC was set up, thus
violating the calling convention once we got to posixCallMainAndExit(). This
then caused any attempt to access global variables here to crash - namely when
setting std.os.linux.elf_aux_maybe.
The fix is to just initialize the ToC manually in _start().
This is problematic for PIE. There's nothing but luck preventing the accesses to
this global variable from requiring relocations. I've observed this being an
issue on MIPS and PowerPC personally, but others may be affected.
Besides, we're really just passing the initial stack pointer value to
posixCallMainAndExit(), so... just do that.
The set of signals that cannot have their action changed is documented in POSIX,
and any additional, non-standard signals are documented by the specific OS. I
see no valid reason why EINVAL should be considered an unpredictable error here.
This reverts commit d7daf7c203f583ed440efc68df6ee690ee8f8f32.
This is no longer needed with the LLVM 18 upgrade, and it was breaking PIE.
Closes#20306.
this one is even harder to document then the last large overhaul.
TLDR;
- split apart Emit.zig into an Emit.zig and a Lower.zig
- created seperate files for the encoding, and now adding a new instruction
is as simple as just adding it to a couple of switch statements and providing the encoding.
- relocs are handled in a more sane maner, and we have a clear defining boundary between
lea_symbol and load_symbol now.
- a lot of different abstractions for things like the stack, memory, registers, and others.
- we're using x86_64's FrameIndex now, which simplifies a lot of the tougher design process.
- a lot more that I don't have the energy to document. at this point, just read the commit itself :p
This adds support for the `-fno-entry` and `-fentry` flags respectively, for
zig build-{exe/lib} and the build system. For `zig cc` we use the `--no-entry`
flag to be compatible with clang and existing tooling.
In `start.zig` we now make the main function optional when the target is
WebAssembly, as to allow for the build-exe command in combination with
`-fno-entry`.
When the execution model is set, and is set to 'reactor', we now verify
when an entry name is given it matches what is expected. When no entry
point is given, we set it to `_initialize` by default. This means the user
will also be met with an error when they use the reactor model, but did
not provide the correct function.
SPARCs have delayed branches, that is, it will unconditionally
run the next instruction following a branch.
Slightly reorder the _start code sequence to prevent it from
accidentally executing stray instructions, which may result in odd
program behavior.
* Replaces the exit assembly with the function from std.
* Reads the top-of-stack struct at program startup that can get information
like the pid.
* Changes the read and write functions to use the Pread and Pwrite syscalls
instead of the depreciated _READ and _WRITE
* Changes the openat function to use flags instead of perms.
Plan9 does not support perms when opening, just when creating.
* Adds an errstr function to read the errstr buf created by the kernel
After fixing some issues with inline assembly in the C backend, the std
cleanups have the side effect of making these functions compatible with
the backend, allowing it to be used on linux without linking libc.
At main startup, if the ELF auxiliary vector contains a stacksize value,
use it as a hint for the minimum stacksize required by the executable.
1. Never lower the hard-limit. Once a hard-limit is lowered, then it can
never be increased (including child processes).
2. If hint exceeds hard-limit then clamp hint to hard-limit.
3. If soft-limit exceeds hint then do nothing.
Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:
* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change
The Wasm backend now supports all features required to use
the full `start.zig` logic, rather than the simplified version.
With this commit we remove all references to the simplified logic
for Wasm specifically.
