Does R use "computed gotos" - a gcc extension of C?
On 03/ 4/11 11:40 PM, luke-tierney at uiowa.edu wrote:
On Fri, 4 Mar 2011, Dr. David Kirkby wrote:
The R manual says R will not build with gcc on 64-bit Solaris x86 with gcc http://cran.r-project.org/doc/manuals/R-admin.html#Solaris "Tests with gcc32 on ?x86? and ?amd64? have been less successful: ?x86? builds have failed on tests using complex arithmetic33, whereas on ?amd64? the builds have failed to complete in several different ways, most recently with relocation errors for libRblas.so. " I know what the "relocation errors" problem is. That library (and in fact two other R libraries) all have non-PIC code in them, despite the fact the source is compiled with the -fPIC option. http://blogs.sun.com/rie/entry/my_relocations_don_t_fit shows how to prove this. If one runs this command on Solaris: $ elfdump -d libRblas.so | fgrep TEXTREL there is some output showing that theres non-PIC code present in the R library. R is compiled with -fPIC on Solaris, but certain things can cause non-PIC code to be generated even with that option. One is by the use of "computed gotos" which is a gcc extension. I'm wondering if R uses any of these.
Yes -- in the byte code interpreter in eval.c luke
Thank you Luke. Do you know if there may be any others?
Do you know if that bit of code gets compiled into all 3 of the R libraries? I
tried replacing
#define NEXT() (__extension__ ({goto *(*pc++).v;}))
by a function which did absolutely nothing. The code built, but still had the
library issues.
I'm almost certain that the definition of NEXT will cause problems, but I'm not
convinced it is the only issue.
What happens if a non-GNU compiler is used? I assume these GNU extensions don't
get used, so how comes the code builds? Is there any way I can disable the use
of the GNU extensions, while still building with gcc.
It is rather annoying that the code has __extension__ in it, which disables the
warnings about the use of GCC extensions.
http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html
Why is there a need to hide the use of the extensions? I'd personally like to
see just standard C used, without any extensions. Then problems like I'm having
would be less likely to occur.
A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? Dave