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When building with a RISC-V kernel with DWARF5 debug info using clang
and the GNU assembler, several instances of the following error appear:
/tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
Dumping the .s file reveals these .uleb128 directives come from
.debug_loc and .debug_ranges:
.Ldebug_loc0:
.byte 4 # DW_LLE_offset_pair
.uleb128 .Lfunc_begin0-.Lfunc_begin0 # starting offset
.uleb128 .Ltmp1-.Lfunc_begin0 # ending offset
.byte 1 # Loc expr size
.byte 90 # DW_OP_reg10
.byte 0 # DW_LLE_end_of_list
.Ldebug_ranges0:
.byte 4 # DW_RLE_offset_pair
.uleb128 .Ltmp6-.Lfunc_begin0 # starting offset
.uleb128 .Ltmp27-.Lfunc_begin0 # ending offset
.byte 4 # DW_RLE_offset_pair
.uleb128 .Ltmp28-.Lfunc_begin0 # starting offset
.uleb128 .Ltmp30-.Lfunc_begin0 # ending offset
.byte 0 # DW_RLE_end_of_list
There is an outstanding binutils issue to support a non-constant operand
to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
be any movement on it, due to concerns over how it would work with
linker relaxation.
To avoid these build errors, prevent DWARF5 from being selected when
using clang and an assembler that does not have support for these symbol
deltas, which can be easily checked in Kconfig with as-instr plus the
small test program from the dwz test suite from the binutils issue.
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
Link: https://github.com/ClangBuiltLinux/linux/issues/1719
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.