[Bug gdb/31048] New: GDB commands very slow due to too many lseek calls

["aditya24.garg at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31048

            Bug ID: 31048
           Summary: GDB commands very slow due to too many lseek calls
           Product: gdb
           Version: 9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: aditya24.garg at gmail dot com
                CC: aditya24.garg at gmail dot com
  Target Milestone: ---

OS: Linux (Ubuntu 20.04.5)

Overview: I have a project consisting of multiple .so files. I have refactored
one of the .so files to a templatized version, therefore now i have quite a few
template classes and functions. Now on using GDB for debugging, commands like
print/ptype are running extremely slow in certain frames. Its taking over a
minute to just execute ptype <namespace::variable-name>

Actual Results: For local args and variables, GDB print/ptype works pretty fast
but with one of the static singleton variables, GDB print/ptype is taking 1
minute to execute. I tried using strace on gdb PID and saw that over 5000 LSEEK
calls for the same offset were being made repeatedly.

From comment on another old ticket
(https://sourceware.org/bugzilla/show_bug.cgi?id=17764#c5), I tried setting
demangle-style to none after which this problem disappeared. Everything became
superfast.

But debugging with mangled names is very inconvenient so i am exploring
solutions to fix this slowness while still using demangler.

Expected Results: Expectation was that GDB will return response within a few
seconds, instead its taking around a minute.

GDB Version: GNU gdb (Ubuntu 9.2-0ubuntu1~20.04.1) 9.2

Environment: 
OS: Linux 5.4.0-135-generic #152-Ubuntu SMP Wed Nov 23 20:19:22 UTC 2022 x86_64
x86_64 x86_64 GNU/Linux

GCC: Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
9.4.0-1ubuntu1~20.04.1' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-9
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-9-Av3uEd/gcc-9-9.4.0/debian/tmp-nvptx/usr,hsa
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.4.0 (Ubuntu 9.4.0-1ubuntu1~20.04.1)

GDB: This GDB was configured as "x86_64-linux-gnu"


Strace Logs:
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
lseek(158, 4980736, SEEK_SET)           = 4980736
ptrace(PTRACE_PEEKTEXT, 865894, 0x7fffe0ccb260, [0x7fffe3a0c920]) = 0
rt_sigaction(SIGINT, {sa_handler=0x556e929a32e0, sa_mask=[INT],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7fb93304d090},
{sa_handler=0x556e929a32e0, sa_mask=[INT], sa_flags=SA_RESTORER|SA_RESTART, s>
brk(0x556ec2ea5000)                     = 0x556ec2ea5000
brk(0x556ec2ec6000)                     = 0x556ec2ec6000
brk(0x556ec2ee7000)                     = 0x556ec2ee7000
brk(0x556ec2f08000)                     = 0x556ec2f08000
brk(0x556ec2f29000)                     = 0x556ec2f29000
brk(0x556ec2f4a000)                     = 0x556ec2f4a000



Interesting fact: When i execute ptype <variable>. It takes 1 minute to run
when current frame selected (lets say frame 5) is from file1.so. And if i go to
frame 10 which belongs to file2.so, then same ptype command executes in 5
seconds. All the changes i have made are for file2.so and no change has been
made to file1.so implementation.

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