[Bug gdb/30525] gdb cannot read shared libraries on SPARC64

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30525

--- Comment #14 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31a56a22c45d76df4c597439f337e3f75ac3065c

commit 31a56a22c45d76df4c597439f337e3f75ac3065c
Author: Pedro Alves <pedro@palves.net>
Date:   Wed Jun 7 10:38:14 2023 +0100

    Linux: Avoid pread64/pwrite64 for high memory addresses (PR gdb/30525)

    Since commit 05c06f318fd9 ("Linux: Access memory even if threads are
    running"), GDB prefers pread64/pwrite64 to access inferior memory
    instead of ptrace.  That change broke reading shared libraries on
    SPARC64 Linux, as reported by PR gdb/30525 ("gdb cannot read shared
    libraries on SPARC64").

    On SPARC64 Linux, surprisingly (to me), userspace shared libraries are
    mapped at high 64-bit addresses:

       (gdb) info sharedlibrary
       Cannot access memory at address 0xfff80001002011e0
       Cannot access memory at address 0xfff80001002011d8
       Cannot access memory at address 0xfff80001002011d8
       From                To                  Syms Read   Shared Object
Library
       0xfff80001000010a0  0xfff8000100021f80  Yes (*)     /lib64/ld-linux.so.2
       (*): Shared library is missing debugging information.

    Those addresses are 64-bit addresses with the high bits set.  When
    interpreted as signed, they're negative.

    The Linux kernel rejects pread64/pwrite64 if the offset argument of
    type off_t (a signed type) is negative, which happens if the memory
    address we're accessing has its high bit set.  See
    linux/fs/read_write.c sys_pread64 and sys_pwrite64 in Linux.

    Thankfully, lseek does not fail in that situation.  So the fix is to
    use the 'lseek + read|write' path if the offset would be negative.

    Fix this in both native GDB and GDBserver.

    Tested on a SPARC64 GNU/Linux and x86-64 GNU/Linux.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30525
    Change-Id: I79c724f918037ea67b7396fadb521bc9d1b10dc5

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