Hi Andrii, On Sat, Mar 4, 2023 at 9:52 AM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Fri, Mar 3, 2023 at 12:37 AM Puranjay Mohan <puranjay12@xxxxxxxxx> wrote: > > > > Parsing of USDT arguments is architecture-specific; on arm it is > > relatively easy since registers used are r[0-10], fp, ip, sp, lr, > > pc. Format is slightly different compared to aarch64; forms are > > > > - "size @ [ reg, #offset ]" for dereferences, for example > > "-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]" > > - "size @ reg" for register values; for example > > "-4@r0" > > - "size @ #value" for raw values; for example > > "-8@#1" > > > > Add support for parsing USDT arguments for ARM architecture. > > > > Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx> > > --- > > You don't mention that in the commit message, but how did you test > these changes? I use the QEMU's virt[1] board with cortex-a15 CPU. I take the libbpf-bootstrap's usdt example[2] and modify it to attach it to my custom program with DTRACE_PROBE1/2/3/4... probes to test different combinations. > > > Changes in V1[1] to V2 > > - Resending as V1 shows up as Superseded in patchwork. > > > > [1] https://patchwork.kernel.org/project/netdevbpf/patch/20230220212741.13515-1-puranjay12@xxxxxxxxx/ > > --- > > tools/lib/bpf/usdt.c | 82 ++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 82 insertions(+) > > > > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c > > index 75b411fc2c77..ef097b882a4d 100644 > > --- a/tools/lib/bpf/usdt.c > > +++ b/tools/lib/bpf/usdt.c > > @@ -1505,6 +1505,88 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec > > return len; > > } > > > > +#elif defined(__arm__) > > + > > +static int calc_pt_regs_off(const char *reg_name) > > +{ > > + int reg_num; > > + > > + if (sscanf(reg_name, "r%d", ®_num) == 1) { > > + if (reg_num >= 0 && reg_num <= 10) > > + return offsetof(struct pt_regs, uregs[reg_num]); > > + } else if (strcmp(reg_name, "fp") == 0) { > > + return offsetof(struct pt_regs, ARM_fp); > > + } else if (strcmp(reg_name, "ip") == 0) { > > + return offsetof(struct pt_regs, ARM_ip); > > + } else if (strcmp(reg_name, "sp") == 0) { > > + return offsetof(struct pt_regs, ARM_sp); > > + } else if (strcmp(reg_name, "lr") == 0) { > > + return offsetof(struct pt_regs, ARM_lr); > > + } else if (strcmp(reg_name, "pc") == 0) { > > + return offsetof(struct pt_regs, ARM_pc); > > + } > > + pr_warn("usdt: unrecognized register '%s'\n", reg_name); > > + return -ENOENT; > > +} > > + > > let's use a more tabular approach, just like, say, riscv does? As R0-R10 directly map to uregs[0->10], I used sscanf for that, and as there are only five named registers (FP, IP, SP, LR, PC), I thought that using if-else would be good enough. But I can change it if it is necessary. > > > +static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg) > > +{ > > + char reg_name[16]; > > + int arg_sz, len, reg_off; > > + long off; > > + > > + if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], #%ld ] %n", &arg_sz, reg_name, > > + &off, &len) == 3) { > > if long function call is wrapped, argument on new line should be > aligned with the first argument on previous line. I'd suggest wrapping > right after format string, and start with &arg_sz aligned with arg_str Will change it in the next version. > > > + /* Memory dereference case, e.g., -4@[fp, #96] */ > > + arg->arg_type = USDT_ARG_REG_DEREF; > > + arg->val_off = off; > > + reg_off = calc_pt_regs_off(reg_name); > > + if (reg_off < 0) > > + return reg_off; > > + arg->reg_off = reg_off; > > + } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) { > > + /* Memory dereference case, e.g., -4@[sp] */ > > + arg->arg_type = USDT_ARG_REG_DEREF; > > + arg->val_off = 0; > > + reg_off = calc_pt_regs_off(reg_name); > > + if (reg_off < 0) > > + return reg_off; > > + arg->reg_off = reg_off; > > + } else if (sscanf(arg_str, " %d @ #%ld %n", &arg_sz, &off, &len) == 2) { > > is the '#<num>' value always in decimal or it could be hex sometimes? I have found all these combinations using trying out different things in my test program as I couldn't find documentation about this. I could not generate a combination where a hex value is returned here. > > > + /* Constant value case, e.g., 4@#5 */ > > + arg->arg_type = USDT_ARG_CONST; > > + arg->val_off = off; > > + arg->reg_off = 0; > > + } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) { > > + /* Register read case, e.g., -8@r4 */ > > + arg->arg_type = USDT_ARG_REG; > > + arg->val_off = 0; > > + reg_off = calc_pt_regs_off(reg_name); > > + if (reg_off < 0) > > + return reg_off; > > + arg->reg_off = reg_off; > > + } else { > > + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str); > > + return -EINVAL; > > + } > > + > > + arg->arg_signed = arg_sz < 0; > > + if (arg_sz < 0) > > + arg_sz = -arg_sz; > > + > > + switch (arg_sz) { > > + case 1: case 2: case 4: case 8: > > + arg->arg_bitshift = 64 - arg_sz * 8; > > + break; > > + default: > > + pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n", > > + arg_num, arg_str, arg_sz); > > + return -EINVAL; > > + } > > This part is repeated verbatim for each architecture, perhaps it's > better to do this post-processing and checking in parse_usdt_spec(). > Would you mind adding another patch to your series that refactors > parse_usdt_arg() implementation to fill out struct usdt_arg_spec and > return arg_sz as out parameter. And then parse_usdt_spec() will check > arg_sz, set arg_signed and arg_bitshift parts? Sure, I will refactor this in the first patch and then add ARM support in the second patch. > > > + > > + return len; > > +} > > + > > #else > > > > static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg) > > -- > > 2.39.1 > > Thanks, Puranjay [1] https://www.qemu.org/docs/master/system/arm/virt.html [2] https://github.com/libbpf/libbpf-bootstrap/blob/master/examples/c/usdt.bpf.c
