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gh-134876: Add fallback for when process_vm_readv fails with ENOSYS#134878
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python-cla-botbot commentedMay 29, 2025 • edited
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All commit authors signed the Contributor License Agreement. |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
I think the those tests are only failing because compilation fails on gcc-10. I'll have a look and see if I can obtain a copy and will update accordingly. |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
Python/remote_debug.h Outdated
| @@ -952,6 +955,38 @@ _Py_RemoteDebug_ReadRemoteMemory(proc_handle_t *handle, uintptr_t remote_address | |||
| result += read_bytes; | |||
| } while ((size_t)read_bytes != local[0].iov_len); | |||
| return 0; | |||
| fallback: | |||
| ; // statement after label needed by gcc 10 and earlier | |||
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Can you factor the fallback out into a different function. I think this makes the normal path more difficult to read
Python/remote_debug.h Outdated
| char mem_file_path[64]; | ||
| off_t offset = 0; | ||
| sprintf(mem_file_path, "/proc/%d/mem", handle->pid); | ||
| int fd = open(mem_file_path, O_RDONLY); |
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This is going to be tremendously inefficient for a profiler because it keeps opening the pseudo file all the time
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I could add the file descriptor toproc_handle_t with an initial value of -1 and then open only on the firstENOSYS. Any thoughts?
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You can guard it with macros for process_vm_readv but we are already checking for they to compile all of this in so you still need to deal with that problem
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Ah no my bad. The problem here is that the function IS defined but the kernel refuses.... alright in that case yeah add it with a guard for only Linux
Python/remote_debug.h Outdated
| result += read_bytes; | ||
| } while ((size_t)read_bytes != local[0].iov_len); | ||
| close(fd); |
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Same as before
Python/remote_debug.h Outdated
| local[0].iov_len = len - result; | ||
| offset = remote_address + result; | ||
| read_bytes = preadv(fd, local, 1, offset); |
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You need to check for preadv and gate it by a macro as this is not available in all platforms IIRC
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I gave this a go, but I think it's making the code a lot more complicated.
I now took a look at the histories of glibc and musl.
In musl, both bothpreadv andprocess_vm_readv were added in 2012 (searches:preadv,process_vm_readv)
In glibcpreadv was added in glibc 2.10 andprocess_vm_readv in glibc 2.15 (man pages:preadv,process_vm_readv). Those were released in 2009 and 2012 respectively. Soprocess_vm_readv is good enough as a guard here.
Seems Android is the one you are thinking of,https://android.googlesource.com/platform/bionic/+/refs/heads/main/libc/include/sys/uio.h
It statespreadv is available at API level 24 andprocess_vm_readv at API level 23, which are from Android 7 (2016) and Android 6 (2015) respectively. I wasn't able to find somewhere stating which versions we support.
I think I will switch topread andpwrite which have been available a lot longer. I tried to do that but I was forever unhappy with the name for the loop-inner count/len variable. I triedto_read,count,len_remaining,bytes_remaining, ... I think I will come back to this tomorrow.
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preadvis available at API level 24 andprocess_vm_readvat API level 23, which are from Android 7 (2016) and Android 6 (2015) respectively. I wasn't able to find somewhere stating which versions we support.
This is defined inAndroid/android-env.sh. Python 3.13 requires API level 21 or greater, and Python 3.14 increases that to 24.
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Given, this, I think is fine, just drop a comment so we know why are we not gating it :)
Python/remote_debugging.c Outdated
| result+=written; | ||
| }while ((size_t)written!=local[0].iov_len); | ||
| return0; | ||
| fallback: |
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Same feedback as the read path
A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated. Once you have made the requested changes, please leave a comment on this pull request containing the phrase |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
@cakemanny one small comment: we squash merge so there is no need to rebase. It's easier to review if you just add commits on top so we don't need to review the full thing every iteration :) |
I have made the requested changes; please review again |
Thanks for making the requested changes! @pablogsal: please review the changes made to this pull request. |
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This adds a fallback
/proc/[pid]/memfrom theproc(5)filesystem whenprocess_vm_readvandprocess_vm_writevare not compiled into the kernel.Regarding tests, these are covered by
./python -m test --match 'test_remote_pdb', but only on affected systems.Do say if this merits a NEWS entry, I wasn't sure because it's a fix for not yet released python versions.