Make "offset" arg to lseek a signed integer #1338
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Otherwise, passing a negative seek amount as a normal Lua number will involve a cast from double to uint64. In C it's undefined behavior when a double outside the [0,2^64) range is cast to uint64. In Lua we try to additionally accomodate the range [-2^63, -1], but there is a bug on x64-64 and might be a bug on other platforms: LuaJIT/LuaJIT#415 However it's cheaper to simply target an int64_t when you want to allow negative numbers, as is our case, because you don't have to do assembly heroics for it to do what you want. The `tonumber` call in the return of `linux.lua:lseek` indicates anyway that our range is not the full 64-bit range, so we might as well restrict instead to long rather than ulong.
dpino
approved these changes
May 3, 2018
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Closing, will reopen as a merge from upstream. |
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Ah, we don't have ljsyscall's history in our repo -- better to reopen this bug, as it's the right thing. |
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This PR merges in a patch to upstream ljsyscall:
justincormack/ljsyscall#224
The original commit log follows:
Otherwise, passing a negative seek amount as a normal Lua number will
involve a cast from double to uint64. In C it's undefined behavior when
a double outside the [0,2^64) range is cast to uint64. In Lua we try to
additionally accomodate the range [-2^63, -1], but there is a bug on
x64-64 and might be a bug on other platforms:
LuaJIT/LuaJIT#415
However it's cheaper to simply target an int64_t when you want to allow
negative numbers, as is our case, because you don't have to do assembly
heroics for it to do what you want. The
tonumbercall in the returnof
linux.lua:lseekindicates anyway that our range is not the full64-bit range, so we might as well restrict instead to long rather than
ulong.