Can anyone explain the use of libc functions _ldtoa_r and _Balloc?

Question

I am working on a project using the Kendryte K210 which is a 64-bit duel-core RISC-V machine. I am using the Kendryte GNU toolchain and the starting point was the Kendryte standalone SDK.

I am experiencing some frustrating core faults. The fault, a misaligned load, is happening after a balr to _Balloc in _ldtoa_r, where a ld instruction in _Balloc is attempting to load from an invalid address pointed to by one of the function argument registers (a0 in this case).

I have been trying to figure out when/where/how _Balloc and _ldtoa_r are used, but they are part of libc. My map file shows _ldtoa_r is somehow related to lib_a-ldtoa.o and lib_a-svfprintf.o and _Balloc is somehow related to lib_a-strtod.o and lib_a-mprec.o. I'm not sure because I am new to interpreting map files.

If anyone can help educate me on what _ldtoa_r and _Balloc are, how they are used, their relationship to these object files, and possibly how to properly interpret relevant lines in the map file, then I would be very grateful.

Thank you.

c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-strtod.o) (_Balloc)

...
 
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-ldtoa.o)
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-svfprintf.o) (_ldtoa_r)

...

 .text._ldtoa_r
0x0000000080027456      0xa74 
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-ldtoa.o)
0x0000000080027456      _ldtoa_r

...

 .text._Balloc
0x000000008002814c       0x6c
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-mprec.o)
0x000000008002814c       _Balloc

...

 .rodata._ldtoa_r.str1.8
0x000000008003cfb8       0x34 
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a(lib_a-ldtoa.o)

Answer 1

Cannyone explain the use of libc functions _ldtoa_r

Is used to convert a long double value to a string, with many customization options, and is reentrant in the Newlib sense takes _REENT state.

It used for example when printing a double value.

https://github.com/bminor/newlib/blob/80cda9bbda04a1e9e3bee5eadf99061ed69ca5fb/newlib/libc/stdlib/dtoa.c

and _Balloc?

Balloc allocate an _Bigint value. _Bigint represents a floating point value as a "big integer".

It is used in various places, mostly when printing and reading a long double values from/to a string.

https://github.com/bminor/newlib/blob/80cda9bbda04a1e9e3bee5eadf99061ed69ca5fb/newlib/libc/stdlib/mprec.c#L97

their relationship to these object files

The compiled code is stored in "these object files".

how to properly interpret relevant lines in the map file

 .text._ldtoa_r
#^^^^^^^^^^^^^^ - section name
0x0000000080027456      0xa74 
#                       ^^^^^ - length of the section
# ^^^^^^^^^^^^^^^ - location of the section in output file
c:/sysgcc/kendryte/bin/../lib/gcc/riscv64-unknown-elf/8.2.0/../../../../riscv64-unknown-elf/lib\libc.a
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - filename
# ..  (lib_a-ldtoa.o)
#      ^^^^^^^^^^^^^  - object filename (used when compiling libc)
0x0000000080027456      _ldtoa_r
#                       ^^^^^^^^ - symbol name
# ^^^^^^^^^^^^^^^^ - location in output file