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| author | Christian Krinitsin <mail@krinitsin.com> | 2025-06-01 21:35:14 +0200 |
|---|---|---|
| committer | Christian Krinitsin <mail@krinitsin.com> | 2025-06-01 21:35:14 +0200 |
| commit | 3e4c5a6261770bced301b5e74233e7866166ea5b (patch) | |
| tree | 9379fddaba693ef8a045da06efee8529baa5f6f4 /gitlab/issues_text/target_missing/host_missing/accel_missing/2448 | |
| parent | e5634e2806195bee44407853c4bf8776f7abfa4f (diff) | |
| download | qemu-analysis-3e4c5a6261770bced301b5e74233e7866166ea5b.tar.gz qemu-analysis-3e4c5a6261770bced301b5e74233e7866166ea5b.zip | |
clean up repository
Diffstat (limited to 'gitlab/issues_text/target_missing/host_missing/accel_missing/2448')
| -rw-r--r-- | gitlab/issues_text/target_missing/host_missing/accel_missing/2448 | 46 |
1 files changed, 0 insertions, 46 deletions
diff --git a/gitlab/issues_text/target_missing/host_missing/accel_missing/2448 b/gitlab/issues_text/target_missing/host_missing/accel_missing/2448 deleted file mode 100644 index 3f791d0d2..000000000 --- a/gitlab/issues_text/target_missing/host_missing/accel_missing/2448 +++ /dev/null @@ -1,46 +0,0 @@ -linux-user as binfmt_misc fails to recognize AT_EXECFD if it's 0 and leaves it open as stdin -Description of problem: -When a `*-linux-user` is used as binfmt_misc, and... - -- The `O` (i.e. open-binary) flag is set -- File descriptor 0 is closed when running the executable - -FD 0 is opened to point at the executable and passed as `AT_EXECFD`, which QEMU fails to recognize and leaves open before handing control over to the executable, leading to the program to think stdin is opened for reading its own executable. - -Some use cases rely on closed stdin to behave correctly. For example, this problem causes the `tests/tail/follow-stdin.sh` and `tests/tac/tac-2-nonseekable.sh` tests in GNU coreutils to fail. In any case, having the executable itself be stdin is definitely incorrect and quite surprising behavior. -Steps to reproduce: -1. Set up qemu-riscv64 as binfmt_misc with `qemu-binfmt-conf.sh`, with the `--credential` flag (which enables open-binary) -2. Get a coreutils built for riscv64 (Let's say it can be found in `riscv64-coreutils/bin`) -3. Run it with something like `riscv64-coreutils/bin/cat <&- | xxd | head` (`xxd | head` to catch the binary output) - -The correct behavior is (You can see by running the native `cat <&-`): - -``` -cat: -: Bad file descriptor -cat: closing standard input: Bad file descriptor -``` - -Instead, the executable `cat` itself is dumped to stdout. - -Perhaps slightly more clear is `riscv64-coreutils/bin/ls -l /proc/self/fd <&-` which shows fd 0 unexpectedly pointing to the coreutils executable. -Additional information: -I'm interested in writing a patch to fix this issue but I'm uncertain how to proceed. This is what I've found so far: - -In `linux-user/main.c` if (effectively) `getauxval(AT_EXECFD)` is 0 it's treated as nonexistent. (https://gitlab.com/qemu-project/qemu/-/blob/0d9f1016d43302108d33d1268304a06cc3fb2021/linux-user/main.c#L758-765) - -```c - execfd = qemu_getauxval(AT_EXECFD); - if (execfd == 0) { - execfd = open(exec_path, O_RDONLY); - if (execfd < 0) { - printf("Error while loading %s: %s\n", exec_path, strerror(errno)); - _exit(EXIT_FAILURE); - } - } -``` - -However as we've seen `getauxval(AT_EXECFD)` can have 0 as a valid value. - -`qemu_getauxval` in `util/getauxval.c` implements several strategies to get the auxv, but doesn't currently give a way to distinguish not found and 0. FreeBSD `elf_aux_info` has `EINVAL` and `ENOENT` error codes but it's ignored here. On Linux, glibc sets `errno` to `ENOENT` to distinguish the two cases but only on glibc >= 2.19. Musl's `getauxval` has always had setting `errno` to `ENOENT`. - -Once we add a proper "`AT_EXECFD` doesn't exist" check this will no longer be a problem since (IIUC) `execfd` will eventually be closed after loading. How should we add "not found" support to `qemu_getauxval`? Is just simply relying on libc's `getauxval` setting `errno` okay? |