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The out-of-block asm() statement carrying _start does not allow the compiler to know what section the assembly code is being emitted to, and there's no easy way to push/pop the current section and restore it. It sometimes causes issues depending on the include files ordering and compiler optimizations. For example if a variable is declared immediately before the asm() block and another one after, the compiler assumes that the current section is still .bss and doesn't re-emit it, making the second variable appear inside the .text section instead. Forcing .bss at the end of the _start block doesn't work either because at certain optimizations the compiler may reorder blocks and will make some real code appear just after this block. A significant number of solutions were attempted, but many of them were still sensitive to section reordering. In the end, the best way to make sure the compiler and assembler agree on the current section is to place this code inside a function. Here the function is directly called _start and configured not to emit a frame-pointer, hence to have no prologue. If some future architectures would still emit some prologue, another working approach consists in naming the function differently and placing the _start label inside the asm statement. But the current solution is simpler. It was tested with nolibc-test at -O,-O0,-O2,-O3,-Os for arm,arm64,i386, mips,riscv,s390 and x86_64. Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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.