On Wed, 2024-02-28 at 10:25 -1000, Richard Henderson wrote: > There are multiple issues with the implementation of shmat(). > > (1) With reserved_va, which is the default for 32-on-64-bit, we mmap > the > entire guest address space. Unlike mmap, shmat refuses to > replace an > existing mapping without setting SHM_REMAP. This is the original > subject of issue #115, though it quicky gets distracted by > something else. > > (2) With target page size > host page size, and a shm area > that is not a multiple of the target page size, we leave > an unmapped hole that the target expects to be mapped. > This is the subject of > > > https://lore.kernel.org/qemu-devel/2no4imvz2zrar5kchz2l3oddqbgpj77jg > wcuf7aritkn2ok763@i2mvpcihztho/ > > wherein qemu itself expects a mapping to exist, and > dies in open_self_maps_2. > > So: reimplement the thing. > > Changes for v2: > - Include Ilya's test case, which caught extra errors: Yay! > - Include x86_64 /proc/self/maps fix, which the test triggers. > - Dropped r-b for the shmat rewrite due to number of changes.
I tested these against our problem with webkitgkt and an happy to report it does solve the segfault we were seeing, thanks! Cheers, Richard
