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If the arg count (excluding > format string) is >3, use bpf_trace_vprintk, otherwise use the older > helper. > > The motivation behind this added complexity - instead of migrating > entirely to bpf_trace_vprintk - is to maintain good developer experience > for users compiling against new libbpf but running on older kernels. > Users who are passing <=3 args to bpf_printk will see no change in their > bytecode. > > __bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF > macros elsewhere in the file - it allows use of bpf_trace_vprintk > without manual conversion of varargs to u64 array. Previous > implementation of bpf_printk macro is moved to __bpf_printk for use by > the new implementation. > > This does change behavior of bpf_printk calls with >3 args in the "new > libbpf, old kernels" scenario. Before this patch, attempting to use 4 > args to bpf_printk results in a compile-time error. After this patch, > using bpf_printk with 4 args results in a trace_vprintk helper call > being emitted and a load-time failure on older kernels. > > Signed-off-by: Dave Marchevsky > --- > tools/lib/bpf/bpf_helpers.h | 45 ++++++++++++++++++++++++++++++------- > 1 file changed, 37 insertions(+), 8 deletions(-) > > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h > index b9987c3efa3c..5f087306cdfe 100644 > --- a/tools/lib/bpf/bpf_helpers.h > +++ b/tools/lib/bpf/bpf_helpers.h > @@ -14,14 +14,6 @@ > #define __type(name, val) typeof(val) *name > #define __array(name, val) typeof(val) *name[] > > -/* Helper macro to print out debug messages */ > -#define bpf_printk(fmt, ...) \ > -({ \ > - char ____fmt[] = fmt; \ > - bpf_trace_printk(____fmt, sizeof(____fmt), \ > - ##__VA_ARGS__); \ > -}) > - > /* > * Helper macro to place programs, maps, license in > * different sections in elf_bpf file. Section names > @@ -224,4 +216,41 @@ enum libbpf_tristate { > ___param, sizeof(___param)); \ > }) > > +/* Helper macro to print out debug messages */ > +#define __bpf_printk(fmt, ...) \ > +({ \ > + char ____fmt[] = fmt; \ > + bpf_trace_printk(____fmt, sizeof(____fmt), \ > + ##__VA_ARGS__); \ > +}) > + > +/* > + * __bpf_vprintk wraps the bpf_trace_vprintk helper with variadic arguments > + * instead of an array of u64. > + */ > +#define __bpf_vprintk(fmt, args...) \ > +({ \ > + static const char ___fmt[] = fmt; \ > + unsigned long long ___param[___bpf_narg(args)]; \ > + \ > + _Pragma("GCC diagnostic push") \ > + _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \ > + ___bpf_fill(___param, args); \ > + _Pragma("GCC diagnostic pop") \ > + \ > + bpf_trace_vprintk(___fmt, sizeof(___fmt), \ > + ___param, sizeof(___param)); \ > +}) > + > +#define ___bpf_pick_printk(...) \ > + ___bpf_nth(_, ##__VA_ARGS__, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \ > + __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \ > + __bpf_vprintk, __bpf_vprintk, __bpf_printk, __bpf_printk, \ > + __bpf_printk, __bpf_printk) > + > +#define bpf_printk(fmt, args...) \ > +({ \ > + ___bpf_pick_printk(args)(fmt, args); \ While looking at test failure related to patch 4, noticed that this isn't handling 0 format arg case correctly, resulting in compilation error. Need to fix and add a test as all extant selftests are doing bpf_printk with at least 1 format arg. > +}) > + > #endif >