-*-org-*-
Alternatively, use debuginfo to generate configure file.
In particular, we could use a config directory, where packages would install their ltrace config scripts. The config file could be named after SONAME, and automatically read when corresponding library is mapped.
A technique used in GDB (and in uprobes, I believe), whereby the instruction under breakpoint is moved somewhere else, and followed by a jump back to original place. When the breakpoint hits, the IP is moved to the displaced instruction, and the process is continued. We avoid all the fuss with singlestepping and reenablement.
This would be useful for replacing the arg1, emt2 etc.
The above format tweaks require that packs that expand to no types at all be supported. If this works, then it should be relatively painless to implement conditionals:
| void ptrace(REQ=enum(PTRACE_TRACEME=0,…), |
| if[REQ==0](pack(),pack(pid_t, void*, void *))) |
This is of course dangerously close to a programming language, and I think ltrace should be careful to stay as simple as possible. (We can hook into Lua, or TinyScheme, or some such if we want more general scripting capabilities. Implementing something ad-hoc is undesirable.) But the above can be nicely expressed by pattern matching:
| void ptrace(REQ=enum[int](…)): |
| [REQ==0] => () |
| [REQ==1 or REQ==2] => (pid_t, void*) |
| [true] => (pid_t, void*, void*); |
Or:
| int open(string, FLAGS=flags[int](O_RDONLY=00,…,O_CREAT=0100,…)): |
| [(FLAGS & 0100) != 0] => (flags[int](S_IRWXU,…)) |
This would still require pretty complete expression evaluation. Including pointer dereferences and such. And e.g. in accept, we need subtraction:
| int accept(int, +struct(short, +array(hex(char), X-2))*, (X=uint)*); |
Perhaps we should hook to something after all.
Some calls result in setting errno. Somehow mark those, and on failure, show errno.
This definitely calls for some general scripting. The goal is to have seconds in adjtimex calls show as e.g. 10s, 1m15s or some such.
Format should take value argument describing the value that should be analyzed. The following overwriting rules would then apply:
| format | format(array(char, zero)*) |
| format(LENS) | X=LENS, format[X] |
The latter expanded form would be canonical.
This depends on named arguments and parameter pack improvements (we need to be able to construct parameter packs that expand to nothing).
Combination of named arguments and some extensions could take care of that:
| void func(X=hide(int*), long*, +pack(X)); |
This would show long* as input argument (i.e. the function could mangle it), and later show the pre-fetched X. The “pack” syntax is utterly undeveloped as of now. The general idea is to produce arguments that expand to some mix of types and values. But maybe all we need is something like
| void func(out int*, long*); |
ltrace would know that out/inout/in arguments are given in the right order, but left pass should display in and inout arguments only, and right pass then out and inout. + would be backward-compatible syntactic sugar, expanded like so:
| void func(int*, int*, +long*, long*); |
| void func(in int*, in int*, out long*, out long*); |
But sometimes we may want to see a different type on the way in and on the way out. E.g. in asprintf, what’s interesting on the way in is the address, but on the way out we want to see buffer contents. Does something like the following make sense?
| void func(X=void*, long*, out string(X)); |
This would be useful for __cxa_throw, presumably also for longjmp (do we handle that at all?) and perhaps a handful of others.
enum-like syntax, except disjunction of several values is assumed.
We currently can’t define time_t on 32bit machines. That mean we can’t describe a range of time-related functions.
Also, don’t format it as characted by default, string lens can do it. Perhaps introduce byte and ubyte and leave ‘char’ as alias of one of those with string lens applied by default.
Really we should keep everything as {u,}int{8,16,32,64} internally, and have long, short and others be translated to one of those according to architecture rules. Maybe this could be achieved by a per-arch config file with typedefs such as:
| typedef ulong = uint8_t |
Or even marked __attribute__((pure)).