musl - [QUESTION] how to gdb dynamic linker for musl?

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Message-ID:
 <OSYP286MB0181BDEBDDD70BF91B18B743FECE0@OSYP286MB0181.JPNP286.PROD.OUTLOOK.COM>
Date: Mon, 7 Dec 2020 21:37:45 +0800
From: "Chen Wang" <unicorn_wang@...look.com>
To: musl <musl@...ts.openwall.com>
Cc: unicorn_wang <unicorn_wang@...look.com>
Subject: [QUESTION] how to gdb dynamic linker for musl?

Hello,
I confugure and make musl with following:

CFLAGS=-g CROSS_COMPILE=riscv64-unknown-linux-gnu- ./configure --prefix=/home/u/ws/musl/install --exec-prefix=/home/u/ws/musl/install --syslibdir=/home/u/ws/musl/install

create the executable with: ./install/bin/musl-gcc -g test.c

Then I tried to debug:
$ qemu-riscv64 -g 1234 ./a.out
then launch gdb:
$ riscv64-unknown-linux-gnu-gdb a.out

but after I tried to target remote, gdb oops and tell me:
```
gdb) target remote:1234
Remote debugging using :1234
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
0x0000004000850ae2 in ?? ()
```

I tried to set sysroot but does NOT take effect:
```
(gdb) set sysroot /home/u/ws/musl/install/
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
(gdb) set sysroot /home/u/ws/musl/install/lib
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
```
I checked the a.out
```
$ riscv64-unknown-linux-gnu-readelf -l a.out
......
  INTERP         0x00000000000001c8 0x00000000000101c8 0x00000000000101c8
                 0x000000000000002d 0x000000000000002d  R      0x1
      [Requesting program interpreter: /home/u/ws/musl/install/ld-musl-riscv64.so.1]
......
```
And I can run with qemu directly: $ qemu-riscv64 ./a.out, this works, but why I can not debug with gdb? Who can help me out? Thanks in adv.

Best Regards

Wang Chen

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