[PATCH v2 0/5] linux-user: Rewrite target_shmat

From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: laurent@vivier.eu, richard.purdie@linuxfoundation.org,
	mjt@tls.msk.ru, iii@linux.ibm.com
Subject: [PATCH v2 0/5] linux-user: Rewrite target_shmat
Date: Wed, 28 Feb 2024 10:25:13 -1000	[thread overview]
Message-ID: <20240228202518.33180-1-richard.henderson@linaro.org> (raw)

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/2no4imvz2zrar5kchz2l3oddqbgpj77jgwcuf7aritkn2ok763@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.

r~

Based-on: <20240222204323.268539-1-richard.henderson@linaro.org>
("[PULL 00/39] tcg and linux-user patch queue")
(Which is technically now out of date, waiting on the coredump
rewrite to solve -Wvla werrors.)

Ilya Leoshkevich (1):
  tests/tcg: Check that shmat() does not break /proc/self/maps

Richard Henderson (4):
  linux-user/x86_64: Handle the vsyscall page in open_self_maps_{2,4}
  linux-user/loongarch64: Remove TARGET_FORCE_SHMLBA
  linux-user: Add strace for shmat
  linux-user: Rewrite target_shmat

 linux-user/loongarch64/target_syscall.h      |   7 -
 linux-user/mmap.c                            | 172 +++++++++++++++----
 linux-user/strace.c                          |  23 +++
 linux-user/syscall.c                         |  16 ++
 tests/tcg/multiarch/linux/linux-shmat-maps.c |  55 ++++++
 linux-user/strace.list                       |   2 +-
 6 files changed, 231 insertions(+), 44 deletions(-)
 create mode 100644 tests/tcg/multiarch/linux/linux-shmat-maps.c

-- 
2.34.1