Integer overflow in `totalSystemMemory` on 32-bit Linux systems

[banshay]

Zig Version

0.15.1

Steps to Reproduce and Observed Behavior

On a system with 96GB of RAM, run:

• zig init
• zig build

Further, when trying to limit memory usage using --maxrss 24G I am very limited as the parsing of this argument returns a usize for a u64. This might be an issue of my system. I ran a little test and usize is a u32.

Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          48 bits physical, 48 bits virtual
  Byte Order:             Little Endian

Expected Behavior

The integer not to overflow or the catch at compiler/build_runner.zig:435 to apply the max u64 as a fallback.

[squeek502]

Could you provide the full error and stack trace?

[banshay]

Sorry, posted from work account. reposting to not confuse

➜  compile-test zig build
thread 14637 panic: integer overflow
/home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib/std/process.zig:1756:34: 0x195c92 in totalSystemMemory (build)
            return info.totalram * info.mem_unit;
                                 ^
/home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib/compiler/build_runner.zig:435:48: 0x18e4c1 in main (build)
        run.max_rss = process.totalSystemMemory() catch std.math.maxInt(u64);
                                               ^
/home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib/std/start.zig:627:37: 0x17b554 in posixCallMainAndExit (build)
            const result = root.main() catch |err| {
                                    ^
/home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib/std/start.zig:232:5: 0x17b20f in _start (build)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following build command crashed:
.zig-cache/o/8cad95c7ce4f2fd5287f26038e9a6dc1/build /home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/zig /home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib /home/user/private/projects/compile-test .zig-cache /home/user/.cache/zig --seed 0x46e7ddfd -Zd5c2671ea36b85c4

[squeek502]

That means the result of info.totalram * info.mem_unit is overflowing a u64, so it seems more likely that something is going wrong (i.e. info is being misinterpreted), since u64 max is more than 18 exabytes.

Could you share more about what OS you're running?

[banshay]

I'm running Windows 11 with WSL2.
uname -r: 6.6.87.2-microsoft-standard-WSL2

On a second pc with the same WSL2 version I don't have the issue. What else could I share?

Edit: maybe a notable difference between the pc where it works and this laptop: The laptop is using shared memory for GPU and RAM.

[squeek502]

You could try editing

/home/user/.cache/zig/p/N-V-__8AADk2yRRtwUe6ef8Fe_YemktCMeO3OFQ80op04uRS/lib/std/process.zig

and insert

std.debug.print("0x{x} * 0x{x}\n", .{ info.totalram, info.mem_unit });

before the return info.totalram * info.mem_unit; line and then run zig build again and see what gets printed (you can revert the change once you're done).

(alternatively, you try using a debugger to see what values info.totalram and info.mem_unit have)

[banshay]

The output is 0xbbb817 * 0x1000

[squeek502]

Hm, the result of that is way below u64 max. Just to be sure, it printed that and then triggered the integer overflow error?

[cryptocode]

totalram is usize on most targets - is usize being 32-bit a possibility in the WSL world?

[squeek502]

Ah, yeah, that's gotta be it. From the OP:

I ran a little test and usize is a u32.

Maybe something like this would fix it?

-            return info.totalram * info.mem_unit;
+            return @as(u64, info.totalram) * info.mem_unit;

[banshay]

Ah, yeah, that's gotta be it. From the OP:

I ran a little test and usize is a u32.

Maybe something like this would fix it?

•        return info.totalram * info.mem_unit;
  

•        return @as(u64, info.totalram) * info.mem_unit;
  

That does indeed fix it.