cmd/gc: allow runtime to define a hex integer type for printing
As part of the translation of the runtime, we need to rewrite
C printf calls to Go print calls. Consider this C printf:
runtime·printf("[signal %x code=%p addr=%p pc=%p]\n",
g->sig, g->sigcode0, g->sigcode1, g->sigpc);
Today the only way to write that in Go is:
print("[signal ")
printhex(uint64(g->sig))
print(" code=")
printhex(uint64(g->sigcode0))
print(" addr=")
printhex(uint64(g->sigcode1))
print(" pc=")
printhex(uint64(g->sigpc))
print("]\n")
(That's nearly exactly what runtime code looked like in C before
I added runtime·printf.)
This CL recognizes the unexported type runtime.hex as an integer
that should be printed in hexadecimal instead of decimal.
It's a little kludgy, but it's restricted to package runtime.
Other packages can define type hex with no effect at all.
Now we can translate that original printf as the more compact:
print("[signal ", hex(g->sig), " code=", hex(g->sigcode0),
" addr=", hex(g->sigcode1), " pc=", hex(g->sigpc), "]\n")
LGTM=r, iant
R=r, iant
CC=golang-codereviews
https://golang.org/cl/
133220043