On Thu, Nov 06, 2014 at 06:40:15PM +0100, Sylvain BERTRAND wrote: > On Thu, Nov 06, 2014 at 05:09:44PM +0000, Dimitris Papastamos wrote: > > On Thu, Nov 06, 2014 at 05:56:55PM +0100, Sylvain BERTRAND wrote: > > > On Thu, Nov 06, 2014 at 03:40:56PM +0000, Dimitris Papastamos wrote: > > > > On Thu, Nov 06, 2014 at 04:38:20PM +0100, Sylvain BERTRAND wrote: > > > > > On a personnal level, I port some of my C99 projects back to C89, > > > > > since it > > > > > seems a C89 compiler is easier to write than a C99 compiler, and some > > > > > part of > > > > > my code could go in C89 only project (i.e. the linux kernel). > > > > > > > > the linux kernel is built with gnu99 iirc. > > > > > > Documentation/HOWTO: > > > "The kernel is written using GNU C and the GNU toolchain. While it > > > adheres to the ISO C89 standard, it uses a number of extensions that are > > > not featured in the standard. The kernel is a freestanding C > > > environment, with no reliance on the standard C library, so some > > > portions of the C standard are not supported. Arbitrary long long > > > divisions and floating point are not allowed. It can sometimes be > > > difficult to understand the assumptions the kernel has on the toolchain > > > and the extensions that it uses, and unfortunately there is no > > > definitive reference for them. Please check the gcc info pages (`info > > > gcc`) for some information on them." > > > > It uses a *lot* of extensions. If I remember correctly, a significant > > number > > of gcc extensions were initially driven by the needs of linux kernel > > programmers. > > > > A C89 only compiler would have no hope to build the kernel in any way > > so I do not see how C89 is relevant here anymore. > > 1 - because it's easier to port to C89/C90 + gnu extensions from C89/C90 than > C99 (moving variable declarations back at the beginning of each block is > already a pain)
There's many instances in the kernel code where variables are not declared at the beginning of the function block.
